# Perpetual Future Mark Price Index

## Perp (Mark) Index Price

The perp index price is a median perp price across supported exchanges, converted from USDT to USD using a median of USDT-USD spot markets.

Perp Exchanges: Binance, OKX, Bybit

Spot Exchanges: Coinbase, Kraken, BinanceUS

Markets: Markets quoted in USDT and converted to USD using median spot price for USDT-USD.

For any asset where Stork provides a mark price, it is calculated as follows:

$Mark Price_{t} = \frac{median(Perp Price_{0t},Perp Price_{1t},...,Perp Price_{nt})}{USDT/USD_{t}}$

where:

PerpPrice(it): Price of asset on exchange i at time t

and:

$USDT/USD_{t} = median(SpotPrice_{0t},SpotPrice_{1t},...,SpotPrice_{nt})$

where:

SpotPrice(it): Price of USDT-USD exchange i at time t

*Note that unlike the index price, every Stork publisher follows the same calculation for the perp index price.*

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