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

# Impact pricing

> How the futures mark is priced from book depth, or from the index when the book is thin

The futures mark follows what it would cost to trade a fixed size on the book, not the best bid
and ask. This is the impact price. A single small order at the top of the book cannot move it.

## Impact notional

The impact notional is **2,000 USDC** on each side, or 2 contracts.

For each side, the venue walks the book from the best price and takes the volume-weighted average
price to fill 2,000 USDC:

* **Impact bid:** the average price to sell 2,000 USDC of notional into the bids.
* **Impact ask:** the average price to buy 2,000 USDC of notional from the asks.

The book price is the midpoint of the two.

## When the book is too thin

If either side cannot fill 2,000 USDC, or the book is crossed, the venue uses the **carry forward**
instead:

```text theme={null}
carry forward = index × (1 + 11.8% × years to expiry)
```

Years to expiry is the seconds left until expiry divided by 365 × 86,400. The carry is simple
interest.

## Limits on the result

Before it becomes the mark, the price is limited in this order:

1. **Basis cap.** It is held within 3% of the carry forward. A one-sided book cannot pull the mark
   far from fair value.
2. **Index band.** It is held inside the [index band](/markets/mark-price-and-bounds#bounds).
3. **Move limit.** It is held within 5% of the previous mark.

The venue applies steps 2 and 3 with a small safety margin, so the chain always accepts the result.

## Cadence

The venue checks every minute and publishes once an hour, the most often the chain allows. It stops
at `last_trade_time`.

## What this means for you

* **Depth moves the mark, not the top of book.** To move the mark, an order has to change the price
  of trading 2,000 USDC.
* **A thin book reverts to carry.** When liquidity is light, the mark tracks the index plus carry.


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