Bid-Ask Spread Cost Calculator

The bid-ask spread is the gap between the highest price a buyer will pay (the bid) and the lowest price a seller will accept (the ask). Market makers and liquidity providers earn this spread in exchange for being available to trade at any time. When you place a market buy order, you fill at or near the ask, above the midpoint. When you sell, you fill at or near the bid, below the midpoint. The difference between where you buy and where you sell is the spread cost: it accrues even with zero-commission brokers, because it is built into the price rather than charged as a fee.

The quoted spread is what you see on the quote screen before the trade: Ask − Bid. The effective spread is 2 × |fill price − midpoint|, calculated after the trade using your actual fill. Effective spread can be smaller than quoted spread if your order receives price improvement, a fill inside the quoted spread, closer to the midpoint. It can be larger if the spread widened between when you sent the order and when it filled, or if your large order moved the market. Comparing the two tells you the quality of your broker's execution.

Limit orders can reduce or eliminate spread cost for the party posting them, but they introduce execution risk. If you post a buy limit at the bid, you pay no spread, but your order may not fill, or may fill slowly while the price moves away from you. If you post a limit at the midpoint, you have a chance of price improvement but an even lower fill probability on a fast-moving stock. The calculator assumes market-order fill prices (ask for buys, bid for sells), which represents the worst-case spread cost for a taker. Limit orders that execute at prices inside the spread will show a smaller effective spread when you use the optional fill-price field.

Divide the dollar spread by the midpoint price, then multiply by 10,000. Example: a $0.05 spread on a $25 stock is ($0.05 / $25) × 10,000 = 20 bps. The same $0.05 spread on a $200 stock is ($0.05 / $200) × 10,000 = 2.5 bps. The dollar spread looks the same, but the cost relative to the price is eight times larger for the cheaper stock. This is why basis points are the right unit for comparing spread costs across securities at different price levels.

Most positions are entered and exited, you pay the half-spread on the way in (buying at the ask) and pay it again on the way out (selling at the bid). The round-trip spread cost is therefore the full spread × shares, not just the half-spread × shares. Traders who think only about entry cost underestimate their true drag. For active traders making dozens of round trips per year, the annualized spread cost can exceed what they pay in commissions, even at "commission-free" brokers where the spread is the primary cost of trading.

Yes for crypto and ETFs, the formulas are identical as long as you enter the correct bid, ask, and number of units. For spot crypto traded on a centralized exchange, enter the bid and ask from the order book and the quantity in coins or tokens. For options, the calculator works mathematically, but interpret with caution: options spreads are typically much wider in basis-point terms (5-50+ bps is common even on liquid options), the midpoint is less reliable as a fair-value estimate, and the dollar size of a contract (100 shares) means even a $0.05 spread per contract represents $5 per contract. Use the "shares" field to enter the number of contracts and remember that each contract controls 100 shares of the underlying.

A round trip is one complete open-and-close cycle: you buy and then sell (or short and cover). The annual round trips field lets you project total spread drag over a year. If you rebalance a position monthly. That is roughly 12 round trips per year. If you are a swing trader turning positions over every week. That is closer to 50. Day traders with multiple positions per day may have hundreds of annual round trips. The annual cost figure is most useful for comparing the impact of trading frequency on total cost, a seemingly small per-trade spread can compound into a significant drag over a year of active trading.

The relevant figure for a specific trade is the spread at the moment the order reaches the market, which is knowable only afterwards. For planning purposes an average or typical spread is a reasonable input, provided it comes from the time of day the trade would actually occur. Spreads at the open and close differ from midday levels, so an all-day average understates cost for some times and overstates it for others.

Spread is one component alongside commissions, exchange or regulatory fees, financing on margin or short positions, and any market impact from size. For a frequently traded position the spread often dominates; for a position held over long periods it can be small relative to financing or to the opportunity cost of the capital. Comparing the spread figure against the expected holding period is what puts it in proportion.