What a round trip really costs
Buying USDT and selling it straight back never returns exactly what you started with. This works out the real gap for any amount, spread and fees included.
Fees here are whatever you type in, not a claim about any specific exchange's current pricing. Check the exchange's own fee schedule before relying on this for a large trade.
Why buying and selling back never breaks even
Two things eat into a round trip. First, the spread: the sell price is always lower than the buy price, because that gap is how a merchant or exchange gets paid for being available to trade with you. Second, any platform or withdrawal fee charged on either leg of the trade, which is on top of the spread rather than instead of it.
Neither of these is unusual or a sign anything is wrong. It is simply the cost of converting currency through a market rather than through a single fixed institutional rate, and it is the same reason changing money at a physical bureau involves a buy price and a sell price that never quite match.
Using this for a real decision
Fill in the actual fee percentages from the exchange you plan to use, not the defaults. The total cost figure above then reflects your real situation rather than a generic estimate, and is worth comparing against the same trade done on a different exchange before committing to either one.