> ## 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.

# Index Price: How Everstrike Calculates Reference Prices

> The Everstrike Index Price aggregates real-time data from 10 spot exchanges with outlier exclusion, underpinning the Mark Price and funding calculations.

The Everstrike Index Price is a derived reference price built from real-time data across a set of major spot exchanges. It updates once per second and serves as the foundation for the [Mark Price](/trading/mark-price), funding rate calculations, and margin requirements. By drawing from multiple independent sources and excluding statistical outliers, the Index Price stays resistant to manipulation on any single venue.

## Constituent Exchanges

The following ten spot exchanges contribute prices to the Index Price calculation:

* Kraken
* Coinbase
* Binance
* Bitfinex
* Kucoin
* Huobi
* Gate.io
* Bitget
* OKX
* Crypto.com

## Outlier Exclusion

Before computing the average, Everstrike identifies and removes outlier prices from the set of constituent exchange prices. This prevents a single exchange experiencing a flash crash, technical issue, or manipulation attempt from distorting the Index Price. The exact outlier threshold and removal methodology are not publicly specified.

## Contract Index Prices

Everstrike calculates a dedicated Index Price for each listed derivatives contract, not just for the underlying asset.

### Perpetual Options

For perpetual options, the Index Price equals the option's intrinsic value. Everstrike derives this intrinsic value from the underlying perpetual futures Index Price.

When the option has no intrinsic value (i.e., it is at-the-money or out-of-the-money), the intrinsic value is zero and Everstrike uses a fallback formula:

```text theme={null}
Option Index Price = 0.05% × Underlying Futures Index Price
```

This ensures the Index Price is always a small positive number rather than zero, which prevents division-by-zero issues in downstream calculations.

**Example:** If the underlying futures Index Price is `$100,000`, the fallback Option Index Price is `$50`.