What is a Liquidity Pool? AMMs Explained in Plain English (2026)

Why DEXs use pools instead of order books#

Traditional exchanges like Coinbase, Kraken, and Binance use order books — sellers post offers, buyers post bids, the exchange matches them. It works well for high-liquidity markets, but it requires a centralized matching engine.

On-chain, running an order book is expensive. Every order placement and cancellation is a transaction with gas cost. For low-volume tokens the market would dry up — nobody wants to post limit orders for tiny altcoins.

In 2018 Automated Market Makers (AMMs) solved this by replacing the order book with a smart contract holding both tokens. Now anyone can swap by interacting with the contract — instant liquidity for any pair, as long as someone has deposited both sides.

How x · y = k actually works — a worked example#

Suppose a Uniswap V2 ETH/USDC pool starts with 100 ETH (x) and 200,000 USDC (y).

The invariant: x · y = k = 20,000,000. Pool price = y / x = $2,000 per ETH.

Now you swap 1 ETH for USDC. The contract must keep x · y = k.

• New x = 101
• New y = 20,000,000 / 101 = 198,019.8
• You receive 200,000 − 198,019.8 = 1,980.2 USDC

Your effective price is $1,980.2 per ETH — slightly worse than the pre-trade $2,000. That gap is slippage, and it gets dramatically worse as your trade size grows relative to the pool. Swapping 50 ETH out of a 100 ETH pool would move the price massively. Swapping 0.1 ETH barely moves it.

How liquidity providers earn fees#

When you deposit tokens into a pool, you receive LP tokens — your proof of share. Every swap charges a fee (0.3% on Uniswap V2, 0.05–1% tiered on V3) that gets added back to the pool reserves. Your LP tokens are now worth slightly more.

A realistic example: in the USDC/ETH 0.05% pool on Uniswap V3, daily volume of $200M generates roughly $100k in fees. If you provide 1% of the pool's liquidity, that's $1,000/day. Annualized it sounds huge — but there's a catch called impermanent loss: when prices move, your LP value can fall behind what you'd have made just holding the two tokens.

Uniswap V2 vs V3 — what changed#

V2's constant product spreads liquidity across an infinite price range (from $0 to infinity per ETH). In practice most trading happens in a narrow band, so V2 wastes most of the capital.

V3 introduced concentrated liquidity: LPs pick a price range, say $1,800–$2,200 for ETH. Inside the range, capital does 100–4,000× more work than V2. The trade-off: if price moves outside the range, your position becomes 100% of the worse-performing token and earns zero fees until price returns.

V3 LPs need active management — narrow ranges plus monitoring, or wider ranges and less efficiency.

What LP tokens actually are#

When you provide liquidity in V2, the contract mints LP tokens (ERC-20s called "Uniswap V2 LP"). They represent your share of the pool. To withdraw, you burn them and the contract returns your share of the current reserves.

LP tokens are themselves valuable. You can stake them in "farms" (Sushiswap, Convex) to earn extra rewards on top of swap fees. This is the foundation of yield farming.

In V3, LP positions are NFTs instead of fungible tokens — each one has a unique range, so they can't all be interchangeable.

Real risks of providing liquidity#

Three categories worth understanding before depositing a cent:

• Impermanent loss. When prices diverge, your LP value lags behind simply holding. At a 2× price move, IL is ~5.7%; at 4×, ~20%; at 10×, ~42%.
• Smart contract risk. Bugs in the pool contract or governance can drain funds. Pick established protocols (Uniswap, Curve) with audits and a long uptime track record.
• Rug pull risk. Pools created by anonymous teams — especially newly-launched memecoins — can be drained by the team removing all liquidity. Only LP into pools with locked liquidity.

Best practices for beginners thinking about LPing#

1. Start with stable-stable pools (USDC/USDT, USDC/DAI). Impermanent loss is near zero, yields are 3–10% APY. Boring but profitable.
2. Move up to correlated pairs like ETH/stETH or BTC/WBTC. Minimal IL, slightly higher yield.
3. Only LP into pools with $5M+ TVL on established protocols. Smaller pools have higher IL volatility and higher rug risk.
4. Use V2 (full range) until you understand V3 trade-offs. V3 narrow ranges require active management or you'll lose to V2 LPs.
5. Track positions weekly. Most LPs lose money because they set and forget. Tools like DeBank or Zerion make this trivial.

For most beginners the better order is: learn buy + HODL first, self-custody second, then experiment with LP later. LPing is a power-user move that punishes inattention.

Bottom line#

Liquidity pools are the engine under every decentralized exchange. The mechanism is elegant: two tokens, a formula, and anyone can trade or supply liquidity without permission. The yields are real but so are the risks — especially impermanent loss on volatile pairs and smart-contract bugs on newer protocols. If you're going to provide liquidity, start with stables on a well-established protocol and scale up only after you've watched a real position through a few weeks of market moves.

Next reads: How to swap tokens on Uniswap · What is DeFi · What is staking.