Providing liquidity and impermanent loss
The most misunderstood concept in DeFi, and the misunderstanding is expensive. The system shows you the loss plainly — and trusts you to do the arithmetic.
This is the most misunderstood concept in DeFi, and the misunderstanding is expensive.
When you provide liquidity to an AMM, you deposit a pair of tokens (say ETH and USDC) and receive LP tokens representing your share, earning a portion of every trading fee the pool collects. The catch is what the pool does to your holdings when prices move.
What the pool does to your holdings
The pool must always satisfy x × y = k, so as the market price of your two tokens changes, it automatically rebalances the ratio you hold. When ETH's price rises on the wider market, arbitrage traders buy the now-cheaper ETH out of your pool until its price matches the market — taking ETH out, putting USDC in. The pool quietly sells your appreciating asset and accumulates the other. You end up with less of the token that went up and more of the one that didn't.
Defining the loss
Impermanent loss is the gap between (a) the value of your pool position and (b) the value those same tokens would have had if you'd simply held them. Because the pool sold your winner on the way up, the pool position is worth less than holding whenever prices diverge from where you deposited.
The math, for a 50/50 pool, as a function of the price ratio r:
IL = 2 × √r / (1 + r) − 1
- A token that doubles (
r = 2) → about −5.7% - A 4× divergence → about −20%
- A 5× divergence → about −25%
The loss grows with divergence in either direction — all that matters is that the two prices move apart.
Why "impermanent"
It's "impermanent" because if prices return to your deposit ratio, the gap closes completely — the loss is only realized if you withdraw while diverged. But it becomes permanent the moment you exit at a divergent ratio, and in practice prices often don't come back.
The honest test is a race: do the fees you earn outweigh the impermanent loss? For a stable, high-volume pair (two stablecoins, barely diverging) fees usually win; for a volatile pair, divergence can dwarf the fees and you'd have been better off holding. (The academic literature reframes this as "loss-versus-rebalancing," but the takeaway is unchanged.)
Why it matters. Impermanent loss is what honesty looks like in an open financial system. The costs of market-making — normally buried inside an institution's books — here become a transparent mathematical consequence you can calculate before you act. The system doesn't protect you from the loss; it shows it to you plainly and trusts you to do the arithmetic.