What is the bid and what is the ask in trading?

The bid is the highest price a buyer will pay for an asset, while the ask is the lowest price a seller will accept; the difference between them is the spread, which represents the market maker's profit.

What is the main difference between the bid price and the ask price?

The main difference is that the bid is always lower than the ask, and the gap between them, called the spread, widens when market volatility rises or liquidity falls, making trades more expensive for you.

Which is better for a buyer: the bid or the ask?

The bid is better for a buyer because it is the lower price, but you typically cannot buy at the bid; to execute an immediate market order, you must pay the higher ask price instead.

Does the bid-ask spread cost me money on every trade?

Yes, the bid-ask spread costs you money on every round-trip trade because you buy at the higher ask and sell at the lower bid, so the asset must move in your favor by at least the spread just to break even.

Is a wide bid-ask spread a risk for investors?

A wide bid-ask spread is a risk because it signals low liquidity and higher transaction costs, which can erode your profits and make it harder to exit a position quickly without accepting a worse price.

How does the bid-ask spread work with limit orders?

With a limit order, you set your own price at or below the current ask for buys or at or above the current bid for sells, so you may wait longer for a fill but you avoid paying the spread entirely.

What is a common beginner mistake with bid and ask prices?

A common beginner mistake is assuming you can buy at the bid and sell at the ask; in reality, you buy at the ask and sell at the bid, and ignoring this reversal leads to unexpected immediate losses on entry.

Are the bid and ask prices the same as the last traded price?

No, the bid and ask prices are not the same as the last traded price; the last price is simply the most recent transaction, while the bid and ask reflect current supply and demand, so they can differ significantly during fast-moving markets.

In a real-world stock trade, when would I use the bid price?

You would use the bid price when selling shares immediately, because that is the highest price a market maker is willing to pay right now; waiting with a limit order above the bid might get you a better fill later.

Can I switch from paying the ask to paying the bid on the same order?

You cannot switch on the same order because it is executed at one price, but you can cancel and place a new limit order at the bid; however, there is no guarantee it will fill if the market moves away from your price.

Difference Between

Difference Between Bid and Ask

Written byNex Virox Team

Editorial Team

Reviewed byVarshal Nirbhavane

Senior SEO & Organic Growth Professional · 5+ years

Published: September 7, 202621 min read

Quick answer

The main difference between Bid and Ask is that the bid is the highest price a buyer will pay, while the ask is the lowest price a seller will accept. Bid is the maximum price a buyer offers for an asset, while Ask is the minimum price a seller requires to part with it. The gap between them is the spread, which represents the transaction cost.

Key takeaways

Core distinction: The bid is the highest price a buyer will pay, while the ask is the lowest price a seller will accept.
How each works: Bid orders execute immediately when matching the ask price, whereas ask orders fill instantly when meeting the bid price.
Cost and performance: The bid-ask spread represents the transaction cost, typically ranging from $0.01 for liquid stocks to several dollars for illiquid options.
Best-fit use case: Use the bid price for market sell orders and the ask price for market buy orders, ensuring immediate execution in active markets.
Most common mistake: Traders often confuse the bid-ask spread with broker fees, but the spread is the market maker's profit, not a commission.

Table of Contents17 sections

Difference Between Bid and Ask: Comparison Table

Aspect	Bid	Ask
Definition	Highest price a buyer will pay for an asset at a given moment.	Lowest price a seller will accept for the same asset simultaneously.
Purpose	Signals maximum willingness to purchase, helping sellers gauge immediate demand.	Signals minimum willingness to sell, helping buyers gauge immediate supply.
Core Mechanism	Buyers submit limit orders; the highest-priced order becomes the visible bid.	Sellers submit limit orders; the lowest-priced order becomes the visible ask.
Price Level	Always lower than the ask in normal market conditions for the same asset.	Always higher than the bid, creating the spread between the two prices.
Market Position	Sits at the top of the order book's buy side, ranked by descending price.	Sits at the bottom of the order book's sell side, ranked by ascending price.
Trader Action	Placing a bid expresses a buyer's intent to acquire an asset at a set price.	Placing an ask expresses a seller's intent to dispose of an asset at a set price.
Execution Trigger	Transaction occurs when a seller accepts the bid or a market sell order arrives.	Transaction occurs when a buyer accepts the ask or a market buy order arrives.
Order Book Side	Occupies the bid side, typically displayed on the left or top of trading screens.	Occupies the ask side, typically displayed on the right or bottom of trading screens.
Price Discovery	Reflects buyer sentiment and perceived value, updating with each new limit order.	Reflects seller sentiment and perceived value, updating with each new limit order.
Liquidity Indicator	Deep bid levels suggest strong buying interest and potential price support.	Deep ask levels suggest strong selling interest and potential price resistance.
Spread Contribution	Lower bid values widen the bid-ask spread, reducing market liquidity.	Higher ask values widen the spread, increasing transaction costs for traders.
Market Maker Role	Market makers quote bids to buy, profiting from the spread when prices move favorably.	Market makers quote asks to sell, profiting from the spread on completed round trips.
Limit Order Type	Buy limit orders create bids, resting until a seller matches the specified price.	Sell limit orders create asks, resting until a buyer matches the specified price.
Market Order Impact	Market sell orders execute against the highest bid, consuming available bid liquidity.	Market buy orders execute against the lowest ask, consuming available ask liquidity.
Price Movement Effect	Rising bids typically push the market price upward as buyers compete aggressively.	Falling asks typically push the market price downward as sellers compete aggressively.
Investor Sentiment	High bids relative to asks indicate bullish sentiment and strong buying pressure.	High asks relative to bids indicate bearish sentiment and strong selling pressure.
Volatility Response	Bids widen sharply during volatile markets as buyers become more cautious.	Asks widen correspondingly during volatility as sellers demand higher premiums.
Time Priority	Earlier bids at the same price receive execution priority over later bids.	Earlier asks at the same price receive execution priority over later asks.
Price Improvement	Buyers can improve bids by raising price, jumping ahead in the order queue.	Sellers can improve asks by lowering price, jumping ahead in the order queue.
Transaction Cost	Buyers pay the ask, not the bid, so the bid represents a potential saving.	Sellers receive the bid, not the ask, so the ask represents potential extra revenue.
Quotation Display	Shown as the lower number in a two-sided quote, e.g., 100.00 bid.	Shown as the higher number in a two-sided quote, e.g., 100.05 ask.
Electronic Trading	Algorithmic buyers adjust bids in microseconds based on market data feeds.	Algorithmic sellers adjust asks in microseconds based on order flow signals.
Forex Market	Bid is the rate at which a dealer buys base currency from a trader.	Ask is the rate at which a dealer sells base currency to a trader.
Options Market	Bid represents the maximum price a buyer pays for an options contract.	Ask represents the minimum price a seller accepts for an options contract.
Bond Market	Bid is the price a dealer pays to purchase a bond from an investor.	Ask is the price a dealer charges to sell a bond to an investor.
Real Estate	Bid is the offer price a prospective homebuyer submits to the seller.	Ask is the listing price the seller sets for the property on the market.
Regulatory Aspect	Best bid and offer rules require brokers to execute at the most favorable bid.	Best bid and offer rules require brokers to execute at the most favorable ask.
Data Availability	Real-time bid data requires exchange feeds or brokerage subscriptions for access.	Real-time ask data requires the same feeds, often bundled with bid data.
Best-Fit Scenario	Use bid when selling assets to know the highest immediate price available.	Use ask when buying assets to know the lowest immediate price available.

What Is Bid?

A bid is the highest price a buyer will pay for an asset at a given moment. It represents immediate demand in a market. The bid exists to facilitate trades by showing sellers the best available offer to sell into right now.

Definition of Bid

A bid is a firm, legally binding quote to purchase a specific quantity of a security, commodity, or currency at a stated price. It is displayed on an order book alongside its size. The bid price always sits below the ask price, creating the spread.

Key Characteristics of Bid

Characteristic	What It Means in Practice
Highest price	The bid is the top price among all active buy orders in the order book at any instant.
Buyer's limit	It caps the maximum amount a buyer is willing to spend per unit of the asset.
Immediate execution	Sellers can hit the bid instantly, guaranteeing a sale at that exact price without delay.
Market depth	Bid sizes at multiple price levels reveal how much buying support exists beneath the current price.
Dynamic value	The bid changes continuously as new buy orders arrive, cancel, or get filled during trading hours.
Spread component	The difference between bid and ask defines the bid-ask spread, a key transaction cost for traders.
Priority rule	Higher bids execute first; if two bids match, the earlier one gets filled before the later one.
Market order trigger	A market sell order always fills at the current best bid, not at a higher price.
Indicator of sentiment	A rising bid suggests increasing buyer aggression; a falling bid signals weakening demand.
Quote precision	Bids are quoted in minimum tick increments, such as $0.01 for stocks or 0.01 pips for forex.

Common Examples of Bid

NYSE stock bid – A trader bids $150.00 for 100 shares of Apple; the order sits at the top of the book until filled.
Forex EUR/USD bid – A dealer quotes a bid of 1.0850, meaning they will buy euros from you at that rate.
Treasury auction bid – An institutional investor submits a competitive bid at 4.25% yield for $10 million in 10-year notes.
Real estate offer – A homebuyer submits a written bid of $350,000 on a listed property, below the seller's asking price.
Used car auction – On Bring a Trailer, a collector places a maximum bid of $45,000 on a classic Porsche 911.
Cryptocurrency exchange – On Coinbase, a limit buy order bids $60,000 for 0.5 Bitcoin, waiting for a seller.
Options market – A trader bids $2.10 for a call option contract, representing the premium they will pay.
Government bond market – A primary dealer bids 99.50 for a $5 million block of 30-year U.S. Treasuries.
Commodity futures – A wheat farmer bids $5.20 per bushel for December futures, locking in a sale price.
IPO book building – An asset manager bids $25 per share for 1 million shares during an initial public offering.

Advantages and Limitations of Bid

Advantages	Limitations
Provides a guaranteed exit price for sellers who want immediate liquidity.	A bid can be cancelled at any time before execution, leaving sellers with no firm commitment.
Reveals real-time buying interest, helping traders gauge short-term demand levels.	The best bid only covers a limited quantity; large orders may move price unfavorably.
Enables price discovery by aggregating all willing buyers into a transparent queue.	Wide bid-ask spreads increase costs, especially for illiquid or volatile assets.
Allows buyers to set a maximum price, preventing overpayment in fast-moving markets.	Bids can be spoofed—fake orders placed to manipulate sentiment without intent to fill.
Creates a two-sided market, which reduces friction and improves overall market efficiency.	In thin markets, the bid may be far below fair value, forcing sellers to accept steep discounts.
Offers a benchmark for valuing positions, as the bid reflects the lowest accepted sale price.	Bids are only valid during trading hours; after-hours quotes may differ significantly.
Supports algorithmic strategies that rely on bid levels for entry and exit decisions.	Latency in quote updates can cause stale bids, leading to missed or mispriced executions.
Enables retail traders to participate with small sizes, as bids are displayed publicly.	Bid prices exclude fees and commissions, so net proceeds are always lower than quoted.
Helps market makers manage inventory by adjusting bids to attract or deter sellers.	A sudden drop in the bid can trigger stop-loss orders, amplifying downward moves.
Provides a clear reference point for negotiating over-the-counter transactions.	Bid depth can vanish during news events, leaving sellers without a reliable floor.

What Is Ask?

The ask is the lowest price a seller will accept for an asset at a given moment. It represents the minimum you must pay to buy immediately, and it exists to facilitate trades by setting a clear, executable seller offer.

Definition of Ask

The ask, or offer price, is the smallest quoted price at which a market participant is willing to sell one unit of a security, commodity, or currency. It is always higher than the bid, and the gap between them forms the bid-ask spread, which measures market liquidity.

Key Characteristics of Ask

Characteristic	What It Means in Practice
Lowest seller price	The ask is the cheapest available price from all active sell orders, so buying at it gives you the best immediate deal.
Always above bid	The ask exceeds the bid by the spread; a wider gap signals lower liquidity and higher trading costs.
Market maker driven	Professional market makers continuously post ask prices to earn the spread, ensuring you can always buy.
Changes with demand	When buying pressure rises, sellers raise asks; when selling pressure dominates, asks fall toward the bid.
Visible on order book	Exchange order books display the best ask at the top, alongside depth showing larger sell orders behind it.
Executable instantly	Market buy orders fill immediately at the current ask, unlike limit orders that wait for a specific price.
Size matters	Each ask has an associated quantity; large orders may exhaust the best ask and move to higher levels.
Time sensitive	Asks are valid only for a moment; fast-moving markets can change the ask multiple times per second.
Different from last trade	The ask reflects current willingness to sell, while the last trade price shows what a past transaction actually paid.
Quoted in ticks	Asks move in minimum increments (e.g., $0.01 for stocks), preventing arbitrarily fine price changes.

Common Examples of Ask

Apple stock (AAPL) – On NASDAQ, the ask might be $192.50 while the bid sits at $192.48, creating a 2-cent spread.
EUR/USD forex pair – A broker quotes an ask of 1.0852, meaning you pay that rate to buy euros with dollars.
Bitcoin (BTC) – On Coinbase, the ask could be $67,890 with a bid of $67,880, reflecting a $10 spread.
US Treasury bond – A 10-year note shows an ask of 98.25, the price you pay per $100 face value.
Gold futures contract – COMEX lists an ask of $2,340.50 per ounce, above the prevailing bid.
Amazon (AMZN) options – A call option has an ask of $4.20, the premium you pay to buy the contract.
Corporate bond – A high-yield issue trades with an ask of 94.75, reflecting a discount to par value.
Ethereum (ETH) – On Binance, the ask is $3,210.15 while the bid is $3,209.85, a 30-cent spread.
Crude oil (WTI) – NYMEX quotes an ask of $78.42 per barrel, above the bid of $78.38.
Japanese yen (JPY) – A currency exchange shows an ask of 0.0067 USD/JPY, the cost to buy one yen.

Advantages and Limitations of Ask

Advantages	Limitations
Provides immediate execution for buyers, eliminating uncertainty about fill prices.	Paying the ask always costs more than the bid, so frequent trading erodes returns through spread costs.
Creates transparent price discovery, showing exactly what sellers demand at any moment.	Thin order books can cause asks to jump sharply, leading to poor fills during volatile periods.
Enables market makers to profit, which keeps markets liquid and reduces overall trading friction.	Wide spreads on illiquid assets mean you may pay a large premium just to enter or exit a position.
Allows limit order traders to set sell targets above current market prices.	Fast-moving asks can change before your order arrives, resulting in slippage on market orders.
Offers a benchmark for valuing assets, as the ask reflects current seller sentiment.	Manipulative traders can post artificial asks to influence perception, creating false resistance levels.
Supports arbitrage opportunities when asks differ across exchanges, aligning global prices.	Large institutional orders can exhaust visible asks, pushing prices higher than retail traders expect.
Provides a clear exit price for sellers who want to know what buyers must pay.	Hidden liquidity means the displayed ask may not reflect true depth, leading to unexpected price moves.
Simplifies market analysis, as the ask forms the upper boundary of the bid-ask spread.	In fast markets, stale asks from cancelled orders can mislead traders relying on real-time quotes.
Enables tight spreads in liquid markets, reducing costs for high-frequency traders.	After-hours trading often shows wider asks due to lower participation, increasing execution costs.
Acts as a reference point for stop-loss orders, helping traders plan exit strategies.	Paying the ask repeatedly in a rising market can cause you to buy at increasingly expensive levels.

Similarities Between Bid and Ask

Shared Aspect	How Bid and Ask Are Alike
Price Quotation	Both the bid and the ask represent the two sides of a single quoted market price for any tradeable asset.
Market Driven	Both the bid and the ask are set by real-time supply and demand forces from active buyers and sellers in the market.
Liquidity Indicators	Both the bid and the ask together reveal the depth of liquidity, showing how easily an asset can be traded.
Transaction Basis	Both the bid and the ask serve as the actual reference prices that determine the execution value of every completed trade.
Exchange Displayed	Both the bid and the ask are always displayed side-by-side on trading screens, order books, and brokerage platforms.
Dynamic Values	Both the bid and the ask fluctuate continuously during trading hours in response to new orders and market news.
Broker Quotes	Both the bid and the ask are provided by market makers or brokers who commit to trading at those stated levels.
Spread Components	Both the bid and the ask are the two necessary components that mathematically define the bid-ask spread.
Order Book Levels	Both the bid and the ask appear as the top levels of the order book, with aggregated pending orders behind them.
Price Discovery	Both the bid and the ask contribute equally to the continuous price discovery mechanism of financial markets.
Currency Denominated	Both the bid and the ask are always quoted in the same base currency or quote currency for a given trading pair.
Time Sensitive	Both the bid and the ask are only valid for a specific moment or short time window, expiring quickly if not filled.
Investor Tools	Both the bid and the ask are essential tools used by retail and institutional investors to plan entry and exit points.
Arbitrage Signals	Both the bid and the ask across different exchanges are compared by traders to spot arbitrage opportunities.
Regulated Data	Both the bid and the ask are subject to financial regulations that require fair and transparent dissemination to the public.
Volume Linked	Both the bid and the ask are typically accompanied by volume figures, showing how many shares or contracts are available at those prices.
Market Sentiment	Both the bid and the ask reflect the collective sentiment of market participants, indicating bullish or bearish pressure.
Technical Analysis	Both the bid and the ask are used by technical analysts to calculate support, resistance, and momentum indicators.
Algorithmic Inputs	Both the bid and the ask are primary inputs for automated trading algorithms that execute high-frequency strategies.
Risk Assessment	Both the bid and the ask help traders assess the immediate risk of slippage, especially in volatile or thin markets.
Fungible Assets	Both the bid and the ask apply equally to fungible assets like stocks, forex pairs, commodities, and cryptocurrencies.
Session Dependent	Both the bid and the ask change based on the trading session, with wider values during off-hours and tighter values during peak times.
Market Maker Commitment	Both the bid and the ask represent a firm commitment from a market maker to buy or sell at those exact quoted prices.
Transaction Cost Basis	Both the bid and the ask are used to calculate the effective transaction cost for any round-trip trade.
Data Feed Standard	Both the bid and the ask are included in standard market data feeds, such as Level 1 quotes, for all listed securities.
Historical Records	Both the bid and the ask are recorded historically, allowing backtesting of trading strategies against past market conditions.
Psychological Levels	Both the bid and the ask often cluster around round numbers or psychological price levels, influencing trader behavior.
Cross-Asset Consistency	Both the bid and the ask follow the same fundamental logic across all asset classes, from equities to derivatives to digital assets.
Execution Necessity	Both the bid and the ask are absolutely necessary for any trade to occur, as a buyer must hit the ask and a seller must hit the bid.

Bid or Ask: Which Should You Choose?

The single variable that decides between the bid and ask price is your role: buyers transact at the ask, while sellers transact at the bid. If you are purchasing an asset, you pay the ask; if you are selling, you receive the bid. The spread between them is the market maker's profit.

When to Use Bid

Choose Bid when you are selling an asset immediately at the current market price. Use the bid for market sell orders, closing long positions, or exiting a trade to lock in profits. The bid is also your reference for limit sell orders placed below the current market to guarantee execution.

When to Use Ask

Choose Ask when you are buying an asset immediately at the current market price. Use the ask for market buy orders, opening new long positions, or covering short positions. The ask is also your reference for limit buy orders placed above the current market to ensure your order fills without delay.

Common Myth	The Reality
"The bid price is what you pay when buying a stock."	The bid is the highest price a buyer offers; you pay the ask, which is the lowest seller's price.
"The ask price is always higher than the bid price."	The ask exceeds the bid by the spread, but in fast-moving markets the spread can widen or narrow dramatically.
"A narrow bid-ask spread means the stock is risky."	A narrow spread signals high liquidity and low risk; wide spreads indicate thin trading and higher uncertainty.
"You can always buy at the bid price if you place a limit order."	A buy limit order at the bid only fills if sellers accept that price; otherwise it sits unfilled until the ask drops.
"The bid-ask spread is the same for all stocks."	Spreads vary by liquidity, volatility, and trading volume; large-cap stocks often have pennies, small-caps can have dollars.
"Market makers always profit from the bid-ask spread."	Market makers profit on average, but they can lose when prices move against their inventory before they rebalance.
"The bid price equals the stock's true value."	The bid reflects the highest immediate buyer interest, not intrinsic value; true value requires fundamental analysis.
"The ask price is the maximum you can sell a stock for."	The ask is the minimum sellers accept; you sell at the bid, which is the highest current buyer's offer.
"Bid and ask prices update only when trades occur."	Bid and ask quotes update continuously from new limit orders and cancellations, even without executed trades.
"A stock with a zero spread has no trading costs."	A zero spread still incurs exchange fees, SEC fees, and possible price impact, so total costs are never zero.
"The bid-ask spread is a broker commission."	The spread is the difference between buyer and seller prices, paid to liquidity providers, not a broker fee.
"You should always use market orders to get the best price."	Market orders fill at the current ask (buy) or bid (sell), often worse than limit orders that wait for better prices.
"The bid price is always lower than the last trade price."	The bid can exceed the last trade if the stock is rising rapidly, as buyers aggressively raise their offers.
"The ask price is always higher than the last trade price."	The ask can fall below the last trade during a sharp decline, as sellers lower their asking prices to exit.
"Bid-ask spreads are fixed percentages set by exchanges."	Exchanges don't set spreads; they emerge from supply and demand, with algorithmic market makers adjusting quotes continuously.
"A wider spread always means you'll lose more money."	A wider spread increases round-trip costs, but it can also signal higher volatility, which may offer larger profit opportunities.
"The bid and ask are the same for every investor."	Institutional investors often see better quotes via dark pools or negotiated trades, while retail sees public NBBO quotes.
"You can buy at the bid and sell at the ask instantly."	Buying at the bid requires a seller willing to transact at that price; selling at the ask needs a buyer at that level.
"The bid-ask spread disappears after market hours."	Spreads persist in after-hours trading but widen significantly due to lower liquidity and fewer participants.
"A stock with a $0.01 spread is always cheaper to trade."	A penny spread on a $5 stock is 0.2% cost, while a penny spread on a $500 stock is only 0.002% — relative cost matters.
"The bid price is the lowest price anyone will sell for."	The bid is the highest price a buyer will pay; the lowest sell price is the ask, which is always higher.
"The ask price is the highest price anyone will pay."	The ask is the lowest price a seller accepts; the highest buyer price is the bid, which sits below the ask.
"Bid-ask spreads are identical across all trading platforms."	Different brokers route orders differently, so you may see slight quote variations, though NBBO provides a unified best price.
"A large spread means the stock is about to crash."	A wide spread indicates uncertainty or low volume, but it doesn't predict direction; it can precede rallies too.
"You can avoid the spread by using a stop-limit order."	Stop-limit orders trigger at the stop price but then fill at the limit price, still subject to the prevailing bid-ask spread.
"The bid-ask spread is the same in bull and bear markets."	Spreads typically widen in bear markets due to higher volatility and reduced liquidity, increasing trading costs.
"The bid price is always shown on the left side of a quote."	By convention, bid appears left and ask right, but some platforms reverse this; always check the label, not position.
"A stock with no bid or ask is untradeable forever."	No quote means no active orders at that moment; new orders can appear within seconds, restoring tradability.
"The spread is the only cost when trading ETFs."	ETFs also incur creation/redemption fees, premium/discount to NAV, and brokerage commissions, adding to total cost.
"Bid-ask spreads are irrelevant for long-term investors."	Spreads still affect entry and exit prices; over decades, even small spreads compound into meaningful performance drag.

Conclusion

Difference Between Bid and Ask comes down to who initiates the trade. The bid is the highest price a buyer will pay; the ask is the lowest price a seller accepts. The spread is your transaction cost. Buy at the ask, sell at the bid. Always use limit orders to control your execution price.

FAQs on Difference Between Bid and Ask

What is the bid and what is the ask in trading?: The bid is the highest price a buyer will pay for an asset, while the ask is the lowest price a seller will accept; the difference between them is the spread, which represents the market maker's profit.
What is the main difference between the bid price and the ask price?: The main difference is that the bid is always lower than the ask, and the gap between them, called the spread, widens when market volatility rises or liquidity falls, making trades more expensive for you.
Which is better for a buyer: the bid or the ask?: The bid is better for a buyer because it is the lower price, but you typically cannot buy at the bid; to execute an immediate market order, you must pay the higher ask price instead.
Does the bid-ask spread cost me money on every trade?: Yes, the bid-ask spread costs you money on every round-trip trade because you buy at the higher ask and sell at the lower bid, so the asset must move in your favor by at least the spread just to break even.
Is a wide bid-ask spread a risk for investors?: A wide bid-ask spread is a risk because it signals low liquidity and higher transaction costs, which can erode your profits and make it harder to exit a position quickly without accepting a worse price.
How does the bid-ask spread work with limit orders?: With a limit order, you set your own price at or below the current ask for buys or at or above the current bid for sells, so you may wait longer for a fill but you avoid paying the spread entirely.
What is a common beginner mistake with bid and ask prices?: A common beginner mistake is assuming you can buy at the bid and sell at the ask; in reality, you buy at the ask and sell at the bid, and ignoring this reversal leads to unexpected immediate losses on entry.
Are the bid and ask prices the same as the last traded price?: No, the bid and ask prices are not the same as the last traded price; the last price is simply the most recent transaction, while the bid and ask reflect current supply and demand, so they can differ significantly during fast-moving markets.
In a real-world stock trade, when would I use the bid price?: You would use the bid price when selling shares immediately, because that is the highest price a market maker is willing to pay right now; waiting with a limit order above the bid might get you a better fill later.
Can I switch from paying the ask to paying the bid on the same order?: You cannot switch on the same order because it is executed at one price, but you can cancel and place a new limit order at the bid; however, there is no guarantee it will fill if the market moves away from your price.