A delta-neutral carry is always told the same way: you buy bitcoin on spot, you sell the same amount in perpetual futures, and the position stops depending on price. Funding lands, the two legs cancel each other out, the trade looks settled. Then a 15% rally arrives in three hours, and the phone shows a liquidation notification.

This is not a contradiction. It is the outcome of a setting most people leave at its default. The margin mode, cross or isolated, decides how much collateral the exchange may seize to rescue a position. It therefore decides the exact price at which the short leg disappears. On a carry, it also decides what is left of the hedge.

The price that matters is not the one on your chart

The first confusion is expensive. An exchange does not liquidate on the last traded price, but on the mark price, a reference price built from the index and an average of the basis. Binance states it plainly: liquidation always happens at the mark price, never at the last price. The goal is to prevent a two second wick on a thin order book from triggering cascading closures.

The practical consequence: the two prices can diverge. A spike on the last price may not liquidate you. Conversely, the mark price can reach your threshold while the candle you are watching still looks far away. If you monitor your position, monitor the mark.

The rule, in one sentence

A position is liquidated when the collateral attached to it, plus its unrealised profit or loss, falls below the maintenance margin. That margin is not a fixed percentage of the capital you deposited, it is a percentage of the position size, called the MMR (maintenance margin rate). It rises in tiers: the larger the notional, the higher the required rate.

In other words, the question is not "how much did I deposit" but "how much size did I open". A well funded account holding an enormous position can be more fragile than a small account holding a small position.

When the threshold is crossed, the exchange closes, charges a liquidation fee, and returns what is left, sometimes nothing. On some venues a partial liquidation happens first, in tiers, to protect the insurance fund more than your position.

Cross margin: one cushion for everyone

In cross mode, the entire futures wallet balance backs every position. A loss on one position reduces the cushion available to the others. The liquidation price of a given position therefore moves constantly, in step with the results of the rest of the account. It is the default mode on most platforms.

The advantage is real: for the same position, the cushion is thicker, so the liquidation price sits further away. The drawback is just as real: one position going badly can take down the whole account, healthy positions included.

One point is often misunderstood in hedged strategies. The spot wallet is not counted in the futures cross wallet. Bitcoin bought on spot does not serve as collateral for your perpetual short. Saying "I am hedged, I hold the spot on the side" does not move your liquidation price by a single centimetre. For the spot gain to protect the short, funds have to be transferred to the futures wallet, which takes time, and often happens at the worst moment.

Isolated margin: one box per position

In isolated mode, each position receives its own margin, separated from the rest. Its maximum loss is capped at that margin: a liquidation does not touch the other positions. The liquidation price stays stable as long as you do not change the allocated margin, the size, or the MMR tier.

The flip side is mechanical: on the same account, an isolated position liquidates earlier than a cross position, because it can no longer draw on the rest of the balance. What isolated mode buys is not safety, it is a boundary. You know exactly what that position can lose, and you know exactly at which price it dies.

Some platforms add margin automatically from the futures wallet. Useful, but it is an option, not a right.

Why the short is almost always the leg that breaks

A carry has two legs, but only one is fragile. The spot leg cannot be liquidated, it can only lose value. The short leg has a hard limit.

The reason is asymmetric: a short loses when price rises, and price has no ceiling. A 30% rally is unremarkable, a 100% fall is impossible. The spot does gain that 30%, but the gain sleeps in another wallet, while the short demands margin immediately.

The worst scenario is also the most common one: squeezes happen when shorts are crowded. Shorts are crowded when funding is high, which is exactly when the carry pays the most. The moment the strategy looks most attractive is therefore the moment the short leg is most exposed to a violent squeeze. A short squeeze is not a theoretical possibility, it is the normal cleanup mechanism of an overcrowded market.

Add ADL risk: when the insurance fund is called upon, the exchange may close profitable positions to balance its books. Your short can disappear while it was nowhere near its liquidation price.

The worked example

Take a short of 1 BTC at 60,000 USDT, with a maintenance margin assumed at 0.5% and fees ignored. The numbers are round, the point is to see the mechanics, not to predict a price.

  • 6,000 USDT of isolated margin: the short liquidates around 65,672 USDT, roughly 9.4% above the entry.
  • Cross margin with a 12,000 USDT balance and no other position: liquidation lands around 71,642 USDT, roughly 19.4% above the entry.

Same entry, same size, same market. Only the mode and the collateral changed, and the death threshold moved by 6,000 USDT. That is all the margin mode does.

The distance reads as the inverse of effective leverage, minus the maintenance margin and fees: 60,000 USDT of notional backed by 6,000 USDT is 10x leverage and a cushion of about 10%. Liquidation fees and the taker rate pull the real price closer still, so any estimate that ignores them is optimistic.

What this changes when you run a carry

A few rules that follow directly from the above.

  • Size the short by risk, not by maximum leverage. If you want the short leg to survive a 30% rally, you need roughly 30% of the notional in margin, plus maintenance. That means effective leverage of 3 at the very most, often less.
  • Keep a buffer in the futures wallet, not only on spot. A buffer of 30 to 50% of the required margin avoids having to transfer funds in the middle of a squeeze.
  • Set alerts at half the distance, not at 90% of the threshold. At 90%, it is already too late to act calmly.
  • Compare funding to risk. Earning a few basis points per eight hour period never justifies a 5% liquidation distance. Funding returns must be read after fees, and next to liquidation risk, not on their own.
  • Write the rule before you open. At this distance, I cut the size. At that one, I add margin. A rule written while calm beats a decision made during a wick.

Four common mistakes

  1. Switching mode with a position open. Platforms refuse the change while a position or an order exists on the contract. The mode is chosen before entry, not after.
  2. Watching the last price. The mark price can be past the threshold while the chart shows something else.
  3. Believing a stop replaces margin. A stop is an order sent to the market. It can slip, or fail to fill in a liquidity gap. The liquidation engine does not read your orders.
  4. Adding margin in a panic without cutting size. Adding margin pushes the threshold away, but increases exposure to an entry that has turned bad if the market does not come back. Cutting size is often the cheaper decision.

How to check before you open

The position page shows an estimated liquidation price. Compare it with the current mark and compute the distance as a percentage. Redo the calculation with the platform's tier table: the MMR is not the same at 20,000 and at 200,000 USDT of notional. Test the mechanism with a tiny size before trusting it with a serious amount, and read your platform's documentation: formulas differ from one exchange to another.

Key takeaways

  • Liquidation triggers on the mark price, when collateral plus unrealised PnL falls below the maintenance margin.
  • Cross shares a cushion, isolated draws a boundary. The first liquidates later, the second liquidates more cleanly.
  • Spot does not collateralise the perpetual: they are two separate wallets.
  • On a carry, the rally is the danger, and it often arrives when funding is at its most attractive.
  • The right question is not the maximum leverage allowed, but the rally your short can absorb.

Sources

Risks

Trading leveraged perpetual contracts carries the risk of losing the entire capital committed, and a liquidation can arrive faster than expected because of the mark price, fees or a tier change. A delta-neutral carry reduces exposure to price direction, it does not remove it: funding can turn negative, the basis can distort, a leg can be liquidated or closed by ADL, and a platform can suspend withdrawals or internal transfers at the worst possible moment. This article describes mechanisms, it is neither investment advice, nor a personal recommendation, nor a promise of returns. Past performance does not guarantee future results. Only commit funds whose loss would not affect your situation.