If you placed an order after seeing 100 USDT but your average fill price was 101.8 USDT, first check the quotes at the time you placed the order and the actual fill details. Price differences and trading fees should be calculated separately.
The spread is the gap between the two current prices
In a hypothetical order book, if the highest bid is 99 USDT and the lowest ask is 100 USDT, the bid-ask spread is 1 USDT. The prices faced by someone looking to buy immediately and someone looking to sell immediately are different. You should also distinguish the most recent traded price shown on screen from the quotes available to trade at now.
The full quantity you want is not available at 100 USDT
Suppose the hypothetical sell orders are as follows. Prices are in USDT per coin, and assume there are no other orders or price changes during the calculation.
2 at 100 USDT / 3 at 101 USDT / 5 at 103 USDT
If you market-buy 10 coins in this situation and your order fills at all three prices, the total cost is (100 × 2) + (101 × 3) + (103 × 5) = 1,018 USDT. The average fill price is 1,018 ÷ 10 = 101.8 USDT.
Using the best ask of 100 USDT you saw initially as the comparison point, the average fill price is 1.8% higher. Compared with the 1,000 USDT you expected to pay for all 10 coins at 100 USDT each, the difference is 18 USDT. In this example, there were fewer coins available to sell at the first price than you wanted to buy, so your order filled at the next price levels too.
Don’t put slippage and fees in the same box
Slippage is the difference between the expected price and the actual fill price. In the example above, 100 USDT was used as the expected price. If you change the comparison point to the most recent traded price or a price at another time, the calculation will also change.
The 1 USDT spread and the 18 USDT difference in total cost are not the same kind of figure. The first is the gap between quoted prices per coin, while the second is the difference in total cost for 10 coins. Don’t simply add them together and call the sum an extra fee. Check the separate transaction details for the actual fee amount and asset deducted by the exchange.
Slippage is affected by liquidity and price movements, and it is not always unfavorable. An order can also fill at a more favorable price. The quotes in this article are illustrative figures to show how the process works; they do not represent actual market conditions or fill results.
What to check before placing an order and after it fills
Before placing an order, check the current spread, how much volume is available at the quoted prices compared with the quantity you want to trade, and the conditions of your order type. A limit order will only fill at your specified price or a better one, but it may take time to fill, fill only partially, or not fill at all. Getting the price you want and getting an immediate fill are separate conditions.
After your order fills, calculate the average price using the price and quantity of each fill, and check the fees separately. If the figures differ from what you expected, check the actual fee deducted and the price difference separately.
Official concept guide: \u003ca-47\u003eBinance Academy — Bid-Ask Spread and Slippage Explained\u003c/a-47\u003e