# Price

### Index Price

The **Index Price** represents the asset price as reported directly by the [Pyth oracle](https://pyth.network/) feed. You can retrieve it from the `price` field in the response of either the [Markets API](/developer-documentation/api/markets.md#retrieve-all-markets-info) or the [Individual Market API.](/developer-documentation/api/markets.md#retrieve-single-market-info)

**Example Response:**

```json
{
  "marketId": "100",
  "symbol": "ETH",
  "skew": "-816032563610058179",
  "price": 2751.21510528,
  "currentOI": "171613599036410749027",
  ...
}
```

### Market Price

The **Mark Price** is a dynamic price adjusted based on open interest skew. You can calculate it using the following formula:

```ts
const indexMultiplier = BigNumber(1e18)
  .plus(
    BigNumber(marketData.skew.toString())
      .dividedBy(marketData.skewScale as string)
      .multipliedBy(1e18)
  );

const markPrice = BigNumber(marketData.price)
  .multipliedBy(indexMultiplier.toString())
  .dividedBy(1e18)
  .toFixed(0);
```

Here, `marketData` is from the response from the [Markets API](/developer-documentation/api/markets.md#retrieve-all-markets-info) or the [Individual Market API](/developer-documentation/api/markets.md#retrieve-single-market-info). 

### Fill price

The **Fill Price** is the most accurate estimate of the execution price for a trade. It accounts for **slippage**, **skew**, and other adjustments, giving you a realistic expectation of what the trade will fill at for a given size. 

You can fetch this value using the [Post-Trade Details AP](/developer-documentation/api/orders.md#fetch-post-order-details)I:

```json
{
  "totalFees": "113173321557870967",
  "fillPrice": "2735468306793171306346",
  ...
}
```

> **Note:** When submitting a trade order, it’s recommended to pass a slightly more aggressive price than the one returned by the Post-Trade Details API. This is because the market can shift between the time you fetch the details and the moment the trade is executed. You can find an example implementation [here](https://github.com/Polynomial-Protocol/polynomial-starter-kit/blob/54aefb1375fdc37ac355d5c1c831de952473ad4c/lib/order.ts#L17).


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