computePriceImpact

Computes the percent difference between the mid price and the execution price of a trade.

Import

import { computePriceImpact } from '@uniswap/sdk-core-next'

Function Signature

function computePriceImpact<TBase extends Currency, TQuote extends Currency>(
  midPrice: Price<TBase, TQuote>,
  inputAmount: CurrencyAmount<TBase>,
  outputAmount: CurrencyAmount<TQuote>
): Percent

Parameters

Name	Type	Description
`midPrice`	`Price<TBase, TQuote>`	The mid price before the trade
`inputAmount`	`CurrencyAmount<TBase>`	The input amount of the trade
`outputAmount`	`CurrencyAmount<TQuote>`	The output amount of the trade

Returns

Percent - The price impact as a percentage (positive means worse execution than mid price).

Formula

priceImpact = (quotedOutput - actualOutput) / quotedOutput

Where:

quotedOutput = midPrice * inputAmount (expected output at mid price)
actualOutput = outputAmount (what you actually receive)

Example

import {
  computePriceImpact,
  Price,
  CurrencyAmount,
  Token,
} from '@uniswap/sdk-core-next'
 
const USDC = new Token(1, '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', 6, 'USDC')
const WETH = new Token(1, '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2', 18, 'WETH')
 
// Mid price: 1 WETH = 2000 USDC
const midPrice = new Price(WETH, USDC, 1n, 2000n)
 
// Trade: Swap 1 WETH
const inputAmount = CurrencyAmount.fromRawAmount(WETH, '1000000000000000000')
 
// Actual output: 1980 USDC (worse than mid price due to slippage)
const outputAmount = CurrencyAmount.fromRawAmount(USDC, 1980_000000n)
 
const priceImpact = computePriceImpact(midPrice, inputAmount, outputAmount)
 
console.log(priceImpact.toSignificant(4)) // "1" (1% price impact)
console.log(priceImpact.toFixed(2))       // "1.00"
 
// Expected: 2000 USDC, Got: 1980 USDC
// Impact = (2000 - 1980) / 2000 = 0.01 = 1%

Use Cases

Trade Warning Thresholds

import { Percent, computePriceImpact } from '@uniswap/sdk-core-next'
 
const LOW_IMPACT = new Percent(1, 100)     // 1%
const MEDIUM_IMPACT = new Percent(3, 100)  // 3%
const HIGH_IMPACT = new Percent(5, 100)    // 5%
 
function getImpactWarning(
  midPrice: Price<Currency, Currency>,
  inputAmount: CurrencyAmount<Currency>,
  outputAmount: CurrencyAmount<Currency>
): 'none' | 'low' | 'medium' | 'high' {
  const impact = computePriceImpact(midPrice, inputAmount, outputAmount)
 
  if (impact.lessThan(LOW_IMPACT)) return 'none'
  if (impact.lessThan(MEDIUM_IMPACT)) return 'low'
  if (impact.lessThan(HIGH_IMPACT)) return 'medium'
  return 'high'
}

With Pool Data

import { Pool } from '@uniswap/v3-sdk-next'
 
async function getTradeImpact(pool: Pool, inputAmount: CurrencyAmount<Token>) {
  // Get mid price from pool
  const midPrice = pool.priceOf(inputAmount.currency)
 
  // Simulate the trade
  const [outputAmount] = await pool.getOutputAmount(inputAmount)
 
  // Calculate impact
  return computePriceImpact(midPrice, inputAmount, outputAmount)
}

Notes

A positive price impact means the execution price is worse than the mid price
Large trades in low liquidity pools will have higher price impact
Price impact is different from slippage tolerance (slippage is the maximum acceptable deviation)