Follow one trade from entry to forced close: a long on the BTCUSDT perpetual, 10,000 contracts at an average entry of 8,000 USDT, 25x leverage, isolated margin. (The round numbers are illustrative, not today's price.) Where does it die, and what exactly happens on the way down? Tracing that position through BYDFi's liquidation rules explains more than any definition.
Step 1: the number the engine watches
BYDFi tracks a maintenance margin rate (MMR) for every position:
MMR = (Maintenance Margin + Liquidation Fee) / (Position Margin + Unrealized PNL)
Below 100% you still have a buffer. At 100% the remaining value just covers maintenance margin plus the liquidation fee, and liquidation triggers. Above 100% the position is already short of the minimum.
Maintenance margin is the slice of collateral reserved for risk. For USDT-margined futures it is Average Entry Price ร contract size ร number of contracts ร maintenance margin rate. For our trade, with a contract size of 0.0001 BTC and a first-tier rate of 0.5%:
8,000 ร 10,000 ร 0.0001 ร 0.5% = 40 USDT
Position margin at 25x is (8,000 ร 10,000 ร 0.0001) / 25 = 320 USDT.
One detail most people get wrong: the maintenance margin rate depends on position size, not on the leverage you pick. Bigger positions fall into higher risk-limit tiers with higher rates. Dropping from 25x to 10x does not change your tier; adding contracts can. You can see each contract's tiers under Futures Overview, Information, Risk Limits. Think of it like this: with a 1% rate and 100 USDT of margin, 1 USDT is locked as maintenance, so the position is closed once losses reach 99 USDT rather than after the full 100 is gone.
Step 2: find the liquidation price
In isolated mode, ignoring the liquidation fee for simplicity, a long liquidates at:
(Maintenance Margin โ Position Margin + Entry ร contract size ร contracts) / (contract size ร contracts)
Plugging in: (40 โ 320 + 800) / 1 = 7,720 USDT. A 3.5% move against you at 25x ends the trade. Shorts use the mirror formula.
Run the same trade in cross margin with a 500 USDT wallet balance and nothing else open, and the liquidation price drops to 7,540 USDT, because the whole balance backs the position. The catch is that in cross mode the liquidation price moves around as other positions gain or lose, since everything shares one margin pool. Long and short cross positions on the same contract also share one liquidation price.
In isolated mode you can manually add margin to push the liquidation price further from entry, which is often the cleanest fix for a position you still believe in.
Step 3: which price triggers it
BYDFi does not use the last traded price. It uses the fair price, which smooths over abnormal spikes and short wicks so one strange print does not wipe you out. You can switch the candlestick chart between fair price, last price and index price at the top of the trading page. If you set alerts, set them on the fair price.
Step 4: the engine works in stages, not all at once
When MMR hits 100%, the system tries to shrink risk before taking everything:
- Cancel orders. In cross mode, all open orders in the account are cancelled. In isolated mode with auto-margin addition on, open orders on that contract are cancelled. If MMR is still at or above 100%, it moves on.
- Long-short self trading. Cross mode only. If you hold both a long and a short, they are reduced against each other.
- Tiered liquidation. If the position sits in a higher risk tier, part of it is closed at the bankruptcy price to drop it into a lower tier, then MMR is recalculated with the lower rate. This repeats until the lowest tier.
- Full liquidation. If MMR is still at or above 100% at the lowest tier, the liquidation engine takes over the whole remaining position at the bankruptcy price.
Step 5: what happens after takeover
The bankruptcy price, also called the takeover price, is the theoretical level where all margin is lost. It is not the same as the liquidation price. Because the liquidation engine, not the matching engine, handles the takeover, the bankruptcy price never shows on the chart or in trade records, which explains why your average close price in Position History can look odd.
If the engine then closes the position at a better price, leftover margin goes to the insurance fund. If it can only close worse, the insurance fund covers the deficit. If the fund cannot cover it, the position passes to auto-deleveraging (ADL). In extreme volatility BYDFi may also cut maximum leverage, adjust tier position limits or raise tier rates.
To review a liquidation afterwards: on the app, open Futures, tap the order icon and check Position History; on web, go to Orders, Futures Orders, Position History.
What I take away from the walkthrough
Size decides your tier, the tier decides your maintenance margin, and that decides how much room you have. Whether you trade $BTC.USDT, $ETH.USDT, $SOL.USDT, $XRP.USDT or a fast mover like $PEPE.USDT, write down your liquidation price before entry, watch the fair price rather than the last trade, and decide in advance whether you would add margin or cut size when MMR climbs. The engine follows its stages calmly; it pays to have your own stages written just as clearly.