> ## Documentation Index
> Fetch the complete documentation index at: https://docs.everstrike.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Mark Price: Manipulation-Resistant Reference Price

> The Everstrike Mark Price drives liquidations and margin calculations. It combines Index Price, order book Fair Price, EMA smoothing, and clamping.

The Everstrike Mark Price is a manipulation-resistant reference price that Everstrike uses to evaluate margin sufficiency and trigger liquidations. Using the Last Traded Price for these purposes would expose traders to deliberate price manipulation — a single large trade could push the price far enough to trigger cascading liquidations. The Mark Price reduces that risk by grounding itself in both external market data and a smoothed view of the order book.

## Calculation Overview

Everstrike calculates the Mark Price in four sequential stages:

1. **Index Price** — derive a reference price from real-time data across selected spot exchanges.
2. **Fair Price** — compute bid and ask impact prices from the order book depth.
3. **EMA smoothing** — apply an exponential moving average to the difference between the Fair Price and Index Price.
4. **Clamping** — constrain the final Mark Price to a permitted range around the Index Price.

## Index Price

The Index Price is the average market price of an asset, calculated from real-time data across a set of selected spot exchanges after excluding statistical outliers. It represents the broader market consensus price and updates once per second.

See [Index Price](/trading/index-price) for the full list of constituent exchanges and how option index prices are derived.

## Fair Price

The Fair Price is derived from two sources: the **Impact Price** (the average fill price at a given order book depth `X`) and the **Scaled Best Price** (a multiplier applied to the current best bid or ask).

For bids:

```text theme={null}
Fair Price (Bid) = Max(Impact Price, Scaled Best Price)
```

For asks:

```text theme={null}
Fair Price (Ask) = Min(Impact Price, Scaled Best Price)
```

Everstrike then averages the two to produce a single Fair Price:

```text theme={null}
Fair Price = (Fair Price (Bid) + Fair Price (Ask)) / 2
```

The impact depth `X` varies by trading pair. For the Bitcoin perpetual futures contract, `X` is currently `0.3 BTC`. You can retrieve the value for each pair from the [Markets API](https://docs.testnet.everstrike.io/#tag/Public/operation/pairs).

## Scaled Best Price

The Scaled Best Price applies a pair-specific multiplier to the current best bid or ask:

```text theme={null}
Scaled Best Price (Bid) = Multiplier × Best Bid
Scaled Best Price (Ask) = Multiplier × Best Ask
```

The multiplier is pair-specific. For the Bitcoin perpetual futures contract it is currently `0.001`. The [Markets API](https://docs.testnet.everstrike.io/#tag/Public/operation/pairs) provides the current multiplier for each trading pair.

## Mark Price Calculation

First, Everstrike calculates the Fair Price basis — the gap between the Fair Price and the Index Price:

```text theme={null}
Fair Price Basis = Fair Price - Index Price
```

It then adds an exponentially smoothed version of that basis to the Index Price:

```text theme={null}
Mark Price = Index Price + EMA_Y(Fair Price Basis)
```

`EMA_Y` is an exponential moving average calculated over `Y` one-second periods. For the Bitcoin perpetual futures contract, `Y` is currently `30`.

Finally, Everstrike clamps the result within a pair-specific permitted range around the Index Price:

```text theme={null}
Mark Price = Min((1 + Z) × Index Price, Max((1 - Z) × Index Price, Mark Price))
```

This keeps the Mark Price between `(1 − Z) × Index Price` and `(1 + Z) × Index Price`.

<Note>
  `Z` is pair-specific. For perpetual futures, `Z` is a fixed percentage. For perpetual options, `Z` is dynamic — Everstrike derives it from the option's Black-Scholes theoretical value and the price of its underlying asset. You can retrieve the current value for each pair from the [Markets API](https://docs.testnet.everstrike.io/#tag/Public/operation/pairs).
</Note>