Token Price Impact Estimator

Buying a long-tail token and watching the chart spike from your own order is the on-chain version of being your own worst enemy.

This estimator uses the constant-product AMM formula (x*y=k) to predict how much a swap of a given size will move the price. Enter the pool's token reserves and your trade size, and it returns the expected output, the effective price you'll pay, and the slippage versus the spot price.

For concentrated liquidity pools (Uniswap v3, etc.), the math is more complex because liquidity is bucketed across price ranges — a v3 pool with concentrated liquidity around the current price will absorb small trades with less slippage than v2-style pools but can punish larger trades when the price moves outside the active range. Use this for v2-style and SushiSwap-style pools, and adjust expectations on v3.

The constant-product math: in a Uniswap v2-style pool with reserves x (input token) and y (output token), trading Δx of the input token gets you Δy where (x + Δx)(y − Δy) = xy. Solve for Δy: Δy = y × Δx / (x + Δx). Without fees, that's the exit. With a 0.3% fee, multiply Δx by 0.997 before applying the formula. Effective price is Δy/Δx. Spot price (the marginal price for an infinitely small trade) is just y/x. Slippage is the percentage difference between effective and spot.

Worked example: a pool has 100,000 USDC and 1,000 of some token (spot price $100). You want to buy with 5,000 USDC. After the 0.3% fee, you're swapping 4,985 USDC. New reserves: USDC=104,985, token=1,000 × 100,000/104,985 = 952.4. You receive 47.6 tokens. Effective price: 5,000 / 47.6 = $105. Slippage: 5%. The spot price after your trade is now 104,985 / 952.4 = $110.23, so you've also moved the chart 10.2% just by buying.

The pain this captures: thinking you're getting 'market price' on an illiquid token. Centralized exchanges have order books that absorb your trade against many small bids; AMMs have one curve, and your trade slides along it. On a $50K-liquidity meme coin, a $5K buy can be 10%+ slippage. New entrants see the chart spike from their own order, get excited, and don't realize they paid a premium for the privilege of being the volume that caused it.

What the basic formula misses: MEV. Sophisticated bots monitor the mempool, see your pending swap, and front-run it — buying just before yours to push the price higher, then selling into your slippage. The result: you pay an effective price worse than the AMM math predicts, and the bot extracts the difference. Real-world impact on thinly traded tokens during peak meme activity can be 1-5% on top of the model. Private mempools (Flashbots Protect, MEV Blocker) help. Higher slippage tolerance does not — it just makes you a juicier target.