MECHANICS Updated 2026-09-12 By Ivo Renner

Binance mark price vs index price: how each one is built

The chart price never liquidates you. That job belongs to a mark price computed from an index that switches between at least five different construction methods depending on what time it is in New York. This is the machinery. It is worth an hour of your attention, because everything else about these contracts is downstream of it.

Why a perpetual needs a synthetic reference price at all

A crypto perpetual has an easy job. Bitcoin trades continuously on many venues, so Binance can average several spot prices and call the result an index. The index is always live because the underlying is always live.

An equity perpetual has a much harder job. Apple trades for six and a half hours a day, five days a week, minus roughly ten US market holidays a year. That is about 32.5 hours out of 168 in a week. For the remaining eighty per cent of the time the contract is open, the thing it references is not printing prices.

But the perpetual never stops. Binance lists these contracts as 24/7, and funding settles on its own clock regardless of whether Nasdaq is open: every eight hours on some symbols, every four on others since the September revision. Positions accrue profit and loss continuously and can be liquidated at any moment. Something has to supply a reference price at 3am on a Sunday, and that something cannot be a live quote, because there is none.

So Binance builds one. The index is an estimate of what the underlying is worth right now, constructed differently depending on how much real information is available. Understanding which mode is active is the single most useful piece of situational awareness you can have on one of these contracts, and it is why we built the session clock.

The index modes, and when each is active

Binance's FAQ describes the index as switching between several construction methods according to the state of the underlying market. There are four session-driven modes plus one that can override them.

Weighted average, updated every second. During regular US trading hours, the index is a weighted average of all constituents, recomputed once per second. This is the high-information regime: real trades, real quotes, minimal inference. If you want your position marked against something close to the actual stock, this is the only window where that is true.

Fast-decay EWMA. In pre-market and after-hours sessions, Binance applies an exponentially weighted moving average with fast decay. An EWMA weights recent observations more heavily than old ones; "fast decay" means old observations lose influence quickly. This is the sensible design for extended hours, where trades do occur but sparsely and at wider spreads — you want to follow real prints without letting a single thin trade jerk the index around.

Slow-decay EWMA. Overnight, the decay slows. Old observations retain influence for longer, so the index becomes stickier and moves less in response to whatever sparse data arrives. The practical translation: in the small hours, the index is mostly a memory of the last session rather than a measurement of the present.

Fixed mode. In this mode no recalculation occurs and the index stays at its last available value. That description remains in Binance's general mode list, but it is not the current weekend rule for equity or commodity TradFi perps: Orderbook EWMA replaced Fixed mode for commodities on 8 May 2026 and for equities on 16 May 2026.

Orderbook EWMA mode. Rather than using unavailable vendor data, Binance averages the Impact Bid Price and Impact Ask Price from its own contract book to obtain an Impact Mid Price, then applies exponential smoothing. The index can therefore move during maintenance, holidays and weekends even though the cash market is shut. This is the current closed-market mode for equity and commodity TradFi perps.

Non-US contracts follow their home calendars. Binance's FAQ gives Hong Kong as 09:30–12:00 and 13:00–16:00 local (UTC+8), Korea's main session as 09:00–15:20 (UTC+9), and mainland China as 09:30–11:30 and 13:00–14:57 (UTC+8). See the non-US guide.

Leaving orderbook mode: the one-minute blend

The transition out of orderbook EWMA mode is the most carefully engineered detail in the whole system, and it tells you what Binance is worried about.

Consider the problem. For an hour, the index has been derived from Binance's own book. Meanwhile the real market reopens and starts printing prices that may be one, two, five per cent away from where Binance's book had settled. If the index switched sources instantaneously, it would step discontinuously, and every stop, every liquidation and every mark-to-market calculation keyed to that index would fire on an artefact of a data-source change rather than on a market move.

So Binance does not switch. On exit from orderbook mode, the FAQ says the index transitions gradually through a weighted blend over roughly one minute, explicitly "to prevent sudden price jumps". For those sixty seconds the index is a moving average of two different constructions, with the weight shifting from the internal one to the external one.

The one-minute window is also, structurally, a period during which the reference price is guaranteed to be wrong in a knowable direction: it is a blend of a stale internal number and a fresh external one, converging on the external one. That is not a trading edge worth chasing at retail scale (the spreads at a reopen will eat it) but it is worth knowing that the number is deliberately in transit rather than measuring anything.

The mark price: a median of three

The index is one input. The mark price is what actually governs your position, and it is computed from the index rather than being the index.

During regular hours Binance computes, once per second:

Mark Price = Median(Price 1, Price 2, Contract Price)

Binance FAQ, Perpetual Futures on Traditional Assets

Two index-derived prices and the contract's own traded price go in; the middle value comes out. Binance's 31 August 2026 update kept this median and changed Price 2's moving-average basis from 30 seconds to one minute. During a non-trading period, the regular median still applies when the index is in Orderbook EWMA mode. Only when an underlying type's index is actually in Fixed mode does Binance replace it with EWMA smoothing of the futures last price.

For current equity and commodity contracts, the weekend case is Orderbook EWMA: the index itself follows a smoothed impact mid from Binance's own book, and the standard median uses that moving index. The underlying cash market still supplies no fresh quote, so Binance order-book conditions have more influence than they do during regular hours. That distinction — a moving internal reference, not a frozen Friday value — is the core hazard covered in trading a US stock at 3am on a Sunday.

Why a median rather than an average

Medians look like an odd choice until you think about what a liquidation engine has to survive.

An average is a democracy of inputs: every value pulls the result toward itself, in proportion to its distance. Feed a bad number into an average and the average moves. Feed a wildly bad number in and it moves a lot. A median does not care about magnitude at all — only about ordering. Two of the three inputs can be sane and the third can be absurd, and the output is unchanged.

That property is exactly what you want when the output triggers forced closures. Three failure modes it defends against:

• A single bad vendor tick. If one index-derived price glitches, the median falls back to the other two. An average would carry the glitch straight into the mark.
• A manipulated order book. If someone drives the contract price violently away from the index (a spoofed sweep through a thin book at 4am) the contract price becomes the outlier and the median ignores it. This is the defence that matters most on low-liquidity contracts. The microcaps and narrow thematic ETFs on the roster are the ones where a determined actor could move the last price; the median means moving the last price is not enough to move everyone's mark.
• A stale feed. If one input freezes while the market moves, it becomes the outlier soon enough and stops governing.

The cost of this robustness is honesty about what the mark price is: it is not the price of anything. It is not the last trade, not the index, not the stock. It is a statistic chosen because it is hard to push around. That is the right design, and it is also why the number your position is marked against will regularly differ from the number on your chart.

The current deviation limits

Binance caps how far the mark price may deviate from the index. The cap is a circuit breaker: it stops a runaway contract price from dragging everyone's mark, and therefore everyone's liquidation level, along with it.

Binance's TradFi FAQ, updated 18 August 2026, gives the current limits below. An older education page previously showed a different regular-hours equity figure; this review uses the product FAQ rather than preserving that stale conflict.

These percentages constrain the mark relative to the index. They are not a cap on trading price, not a maximum possible loss and not a promise that liquidation cannot occur inside the band. Binance also reserves the right to change the constraints during extreme market conditions.

Why the mark price is what liquidates you

On Binance, unrealised profit and loss and the liquidation trigger are both computed from the mark price. The last traded price is not used for either. This is not a TradFi-perpetual quirk (it is standard across USDⓈ-M futures) but it bites harder here because of how far the mark can sit from the last price outside US hours.

The reasoning is straightforward. If liquidations keyed off the last traded price, then in a thin book a single aggressive order could sweep down through resting bids, print a low price, trigger liquidations, and those liquidations would themselves sell into the book, printing lower prices and triggering more. A cascade started by one order. Marking against a median-based, deviation-capped, index-anchored price breaks that loop: to move everyone's mark you would have to move the index, and to move the index you would have to move the underlying market.

Three consequences you should hold onto:

1. Your liquidation price is a mark-price level, not a chart level. A wick on the candle chart that touches your liquidation price may not liquidate you, because the mark did not follow it. Equally, you can be liquidated without the chart appearing to reach your level. Work your levels in mark-price terms — the liquidation price calculator assumes exactly this.
2. Stop orders and liquidation may use different triggers. Binance lets you choose the trigger for conditional orders. If your stop is set to last price and your liquidation runs on mark price, they can fire in the wrong order — the protection you set may sit behind the event it was meant to protect against. Check the trigger setting on every conditional order.
3. Outside US hours, mark and last can diverge more. The index may be smoothed from vendor observations or, when external data is unavailable, derived from a smoothed impact mid in Binance's own book. The contract price is live. That is when a chart level and a margin level are least likely to mean the same thing.

The weekend band, with numbers in it

Two of the mechanics above interact over a weekend, and the result is worth deriving once by hand. Take a contract whose index is 200.00 when the cash market closes — a round figure chosen for arithmetic, not a quotation. Orderbook EWMA can keep moving that index while the stock market is shut.

Suppose weekend order-book activity moves the smoothed index to 202.00. The published ±3% weekend constraint is now centred on that moving index, giving 195.94 to 208.06 at that instant. If the last traded price reaches 214.00, that does not make 214.00 the mark, and it does not freeze the index at 200.00.

Which number answers which question

The stop row is the one you choose. The deviation band is not relief: on Monday the index transitions from order-book input toward live stock-market data, and the reference can move sharply during that blend.

The 31 August mark-price change is in force

Binance published Important Updates on Mark Price Calculation of TradFi Perpetual Contracts on 28 August 2026, effective 31 August at 08:15 UTC. It kept Mark Price = Median (Price 1, Price 2, Contract Price) and changed Price 2's moving-average basis from 30 data points over 30 seconds to 60 data points over one minute.

We opened and checked that announcement on 11 September 2026. The change is narrower than the old placeholder on this page implied, but it confirms that the calculation can be revised quickly. Read the live FAQ and symbol parameters periodically rather than learning the mechanism once.