Maintenance margin is the smallest fraction of a position's notional value that must remain in your account as collateral. Fall to it and the position is liquidated. On major crypto exchanges it starts near 0.4% to 0.5% for small BTC perpetual positions and rises with position size through a tier schedule.
01Tiers and why they exist
The tier schedule ties the maintenance requirement to notional. A small position pays a low rate because it can be closed quickly without moving the market. A position worth tens of millions demands several percent or more, because closing it will eat depth and the exchange needs a bigger buffer against slippage.
Each tier defines three things: the maintenance rate, the maximum leverage allowed, and the notional ceiling. Crossing a ceiling while holding a position can trigger liquidation by itself, even without an adverse price move.
02Initial versus maintenance
Initial margin is what you post to open the position, equal to 1 divided by leverage. Maintenance margin is the floor below which the position dies. The gap between them is your room to be wrong. At 10x the initial margin is 10%, so with a 0.5% maintenance rate you can lose roughly 9.5% of notional before liquidation.