The bid-ask spread helps explain why immediately buying and selling can return less even without a change in the best quotes. Use two prices, a defined quantity and time, then add fees separately. The examples below are hypothetical arithmetic, not current prices or an invitation to trade.
Assumes enough quantity and unchanged quotes for both trades.
BTKWIN.COM · EDUCATIONAL EXAMPLEBid, ask and last trade have different meanings
Best bid is the highest currently displayed buy request, while best ask is the lowest sell offer in the ordinary book model. An immediate buy normally encounters asks and an immediate sell bids, subject to actual quantity and instructions.
Last trade records what already happened. A chart showing 99.8 does not establish that you can buy and sell at 99.8 now when bid is 99.5 and ask 100.
The midpoint is another reference, not necessarily an executable offer. State which field is used before comparing costs or declaring that a displayed current price failed to match execution.
A 0.5-percent example without a new market move
Assume one unit is available to buy at 100 and sell at 99.5, with those quotes unchanged and fees excluded. Buying and then selling returns 0.5 fewer quote units.
Relative to the 100 purchase cost, that difference is 0.5%. The result comes from crossing between sides under these assumptions, without requiring a further decline in quotes.
It is not a prediction that every real purchase loses this fraction. Later prices, available quantity and execution can differ. Keep the static illustration separate from an actual market outcome.
Name the denominator
| Measure | Hypothetical calculation | Result |
|---|---|---|
| Absolute spread | 100 − 99.5 | 0.5 |
| Round-trip loss relative to buy cost | 0.5 ÷ 100 × 100 | 0.5% |
| Midpoint | (100 + 99.5) ÷ 2 | 99.75 |
| Spread relative to midpoint | 0.5 ÷ 99.75 × 100 | About 0.5013% |
Different percentages need not indicate an error
The midpoint-based result differs because its denominator is 99.75 rather than 100. Before comparing interface percentages, read each definition instead of treating any difference as a faulty calculation.
Check percentage versus basis points too. One basis point is 0.01 percentage point, so 0.5% is 50 basis points. Entering 50 into a percentage field rather than a basis-point field changes the intended scale.
A useful note records price source, time, quantity and denominator. Without them a precise-looking spread figure can be ambiguous even if every arithmetic step is correct.
Add each trading fee to the appropriate value
Assume an educational 0.1% quote-currency commission on both trades. Buy fee on 100 is 0.1, making actual outlay 100.1. Sell fee on 99.5 is 0.0995, leaving 99.4005.
Total difference is 0.6995. Relative to actual outlay 100.1, the loss is about 0.6988%. This uses each actual trade value instead of simply adding rounded percentages.
These are not current rates. If the buy fee is deducted from base quantity, you may no longer have a full unit to sell. Recompute with actual net quantity and the proper fee asset.
A tight top spread can conceal limited depth
Suppose one unit is offered at 100 and two more at 101 while best bid is 99.9. Buying three in that fixed example costs 302, or about 100.6667 average before commission.
The best ask does not cover all three. Do not attribute the complete difference from three times 100 to the quoted top spread; crossing depth levels contributes a separate execution effect.
To estimate the corresponding sell, inspect bid quantities independently rather than assuming the same depth on both sides. Our order book guide explains level and cumulative quantity.
Compare complete offers on an equivalent basis
Align pair, quote currency, quantity, product and observation time. A coin against fiat is not silently the same as the coin against a stablecoin, and an older snapshot can measure market movement rather than a provider difference.
For a hypothetical one-unit purchase, price 100 plus a 0.2% quote fee totals 100.2. Price 100.1 plus a 0.05% fee totals 100.15005. The lower raw price is not the lower complete cost under those assumptions.
Only include withdrawal, deposit and conversion costs if those steps are necessary for the compared purpose. A venue price gap does not automatically produce executable profit once access, time, transferability and fees are considered.
A limit order controls price without guaranteeing completion
A limit below current opposite offers may wait unfilled. A limit allowing immediate matching can cross the book and take liquidity. Choosing Limit does not automatically eliminate spread effects or establish maker treatment.
Compare completed outcomes with completed outcomes. A cheaper unfilled order is not an acquired holding or guaranteed alternative purchase. Use actual filled quantity, weighted price and commission to explain past results.
Our partial fill guide helps preserve that distinction when only some quantity trades. The unfilled remainder belongs in a separate state and calculation.
Review the evidence behind an immediate loss display
Record best bid and ask with time, actual fills, fee asset and net quantity. Distinguish spread from price movement, crossing levels and independent deductions.
Zero commission does not guarantee a costless buy-and-sell route. A quoted conversion interface can also incorporate its own pricing method rather than exposing an order book. Read the actual product’s explanation.
A wide spread alone does not establish manipulation or a platform-safety conclusion. It describes a relationship between relevant quotes at an observed time and quantity context, with further evidence needed for stronger claims.
Keep transfer questions separate
A trade exchanges assets within its trading system; a withdrawal sends holdings through another route with its own conditions. If an external balance is missing, inspect network and transaction evidence instead of searching the spread calculation for the cause.
The cost tool organizes necessary route charges and the help tool identifies execution versus crediting stages. Neither turns a static spread example into a forecast.
The reviewable conclusion explains actual quantity, relevant prices, fee treatment and comparison basis. That is more useful than relying on one current-price label or treating a small percentage as a complete account of execution.
Keep the quote currency explicit
Write the currency beside each price and total. A similar numerical spread in two different quote assets is not automatically the same cost, especially if converting the proceeds requires another transaction or service charge.
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English content and examples reviewed: 27 October 2026. Read the Arabic edition.
