When swapping from your wallet, use a constant-product curve to estimate how a trade will move the pool price. The reserve ratio gives the starting marginal price, but a real trade changes that ratio as it takes tokens out. Your average execution price can therefore be worse, especially in a shallow pool.
A constant-product pool sets its starting marginal price from the ratio of its token reserves. “Marginal price” means the rate for a very small next trade, before that trade meaningfully changes the pool.
In a V2 liquidity pool, the two reserves are multiplied: x × y = k. Here, x and y are the amounts of each token, and k stays roughly constant during a swap. If a pool holds 100 ETH and 200,000 USDC, its starting price is about 2,000 USDC per ETH.
That ratio is a spot estimate, like the best visible price on a centralised exchange. It does not promise that you can buy a large amount at that rate. Each token you add or remove changes the reserve ratio, so the next unit trades at a different price.
Your execution price is the average rate across the whole trade, so it moves along the curve. Consider two illustrative swaps into the same 100 ETH and 200,000 USDC pool: one for 1 ETH and one for 10 ETH. Assume no fee in these examples to isolate the curve’s effect.
For 1 ETH in, the pool returns about 1,980 USDC. That is an average of about 1,980 USDC per ETH, below the 2,000 starting price; after the swap, the marginal price is about 1,961. For 10 ETH in, it returns about 18,182 USDC, or roughly 1,818 per ETH, and the new marginal price falls to about 1,653.
The larger swap gets a worse average price because it consumes more of the pool’s available USDC. This curve-driven change is called price impact. A pool’s depth—the size of its reserves—sets how quickly impact grows; the same trade usually moves a deeper pool less.
Real pools charge a swap fee, which reduces the input used in the curve calculation; the fee rate depends on the pool. So compare the expected output after fees and price impact, rather than comparing only the displayed spot price. For a Base wallet swap, BaseSwap is one venue to consider; the constant-product explanation applies to pools that use this design.
Check the pool reserves and the trade’s expected output to judge whether the price impact fits your plan. If a route uses several pools, each pool adds its own curve movement and may add a fee, so the final output can differ from a single-pool estimate.
A useful edge case is a trade that looks small in dollars but is large compared with one reserve. A $2,000 buy against a deep pool may barely shift the ratio; the same buy against a pool with only a few thousand dollars of liquidity can move it sharply. Check the trade size against pool depth, not just your wallet balance.
BaseSwap is a decentralized exchange on Base where you can swap tokens. Before confirming any wallet swap, I’d check: