Margin = size ÷ leverage
The margin you post is just your position size divided by leverage. The trap is that higher leverage posts less margin but moves your liquidation closer — at 10x a ~9% move wipes the margin, at 50x under 2%. Don't confuse cheap margin with safe. See exactly where you get wiped with the liquidation calculator, pick leverage from the move you expect with the leverage liquidation table, and size from risk with the position size calculator.
Margin is what you post — not what you risk
On isolated margin, the collateral you put up is the maximum you can lose on that position. Post $100, leverage 10x, notional $1,000 — you lose $100 max (plus fees) if the trade goes to liquidation. Cross margin works differently: your entire available balance backs all positions, so a single big loss can wipe accounts you thought were separate.
Initial margin = notional ÷ leverage. At 10x, $1,000 notional needs $100 initial margin. Maintenance margin is lower — typically 0.5% of notional, so $5 on a $1,000 position. When your margin drops to $5 via losses, liquidation triggers.
Adding to a position increases margin requirement proportionally. Going from $100 collateral to $150 doesn't move your liquidation price if the new units were bought at the same entry — it just increases your notional exposure. On cross margin, the freed balance from unrealized gains can be used as margin, which is how people accidentally over-lever.
Related: liquidation price, effective leverage, maintenance margin.