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

# Impact Pricing

> How Phoenix uses order book impact to price real-world asset perps when external markets are closed

Impact pricing is Phoenix's internal pricing mechanism for real-world asset perp markets when external markets are closed.

It uses Phoenix order book liquidity to move the last known external oracle price gradually, instead of freezing the index price until the next external session.

## Book Impact

With previous oracle price `S`, Phoenix calculates the price impact of crossing a configured notional amount against the order book:

*Book Impact Price* = *max*(*ImpactBid* - S, 0) - *max*(S - *ImpactAsk*, 0)

where `ImpactBid` and `ImpactAsk` are the average execution prices for selling and buying `$1000` notional, respectively. The configured notional is currently `$1000` and is subject to change.

If one side of the book does not have enough depth for the configured notional, that side contributes `0` to the impact calculation.

## EMA Update

Phoenix adds the book impact price to the previous oracle price to form a target price:

*Target Price* = S + *Book Impact Price*

The internal oracle then moves toward the target using a continuous-time EMA. The default EMA time constant is 1 hour.

## Bounds

For real-world asset markets in internal pricing periods, Phoenix applies the market's configured price bounds before emitting the internal price.

The bound is set around the last known external index price. For example, a market with 20x maximum leverage has a 5% bound, while a market with 25x maximum leverage has a 4% bound.