Only looking at the best bid and best ask can make it seem too easy to account for a single trade.
For example, suppose the best sell is 10.00 USDT and the best buy is 9.90 USDT. If you use 1000 USDT to buy 100 units and then immediately sell at the best bid, the gross proceeds are only 990—the 10 USDT difference first gets eaten up by the price gap. Now assume both the buy and sell each charge 0.1%. The fees on the two sides are 1 and 0.99 USDT, totaling 11.99 USDT less, and this still doesn’t include slippage. The price gap is only the distance between quotes; it can’t replace the full round-trip cost.
Before placing an order, write in one line the buy amount, the planned sell price, the fees on both sides, and the slippage you’re allowing for. Then recalculate using “sell proceeds − total cost,” and decide whether to place the order.
For example, suppose the best sell is 10.00 USDT and the best buy is 9.90 USDT. If you use 1000 USDT to buy 100 units and then immediately sell at the best bid, the gross proceeds are only 990—the 10 USDT difference first gets eaten up by the price gap. Now assume both the buy and sell each charge 0.1%. The fees on the two sides are 1 and 0.99 USDT, totaling 11.99 USDT less, and this still doesn’t include slippage. The price gap is only the distance between quotes; it can’t replace the full round-trip cost.
Before placing an order, write in one line the buy amount, the planned sell price, the fees on both sides, and the slippage you’re allowing for. Then recalculate using “sell proceeds − total cost,” and decide whether to place the order.