How close it really is
Your initial margin is 1 ÷ leverage of the position — at 10× that is 10% of the notional. The exchange closes you out slightly before that margin is gone, once equity drops to the maintenance requirement. So the move you can absorb is (1 ÷ leverage) − maintenance margin, and at 10× with 0.5% maintenance that is 9.5%, not 10%.
The numbers get uncomfortable quickly. At 20× you have 4.5% of room. At 50× you have 1.5%. At 100× you have 0.5% — which Bitcoin can cover in under a minute on an ordinary day, and has covered in seconds on a bad one.
Why your exchange may say something slightly different
Three reasons, all worth knowing before you rely on any calculator including this one.
- Maintenance margin is tiered. It rises with position size — a large position on the same pair carries a higher requirement and therefore a nearer liquidation. Check your exchange's tier table rather than assuming the default.
- Cross margin changes the question. This calculator assumes isolated margin, where the position can only draw on the margin assigned to it. Under cross margin your whole balance backs the position, so liquidation is further away — until it takes the account with it.
- Funding and fees eat margin over time. On a perpetual, funding is charged every few hours. A position held for days drifts towards liquidation even if price never moves.