Liquidity Pools and LP Tokens: Becoming the Market

So far you’ve been the trader — the one walking up to the pool and swapping ETH for USDC. But somebody had to fill that pool first, and the formula doesn’t conjure tokens out of thin air. The reserves come from liquidity providers (LPs): ordinary users who park both tokens in the contract so traders have something to trade against. In return, every swap’s 0.3% fee drips into reserves they own a slice of.

This lesson flips you to the other side of the counter. You stop trading against the pool and start being the pool. We’ll cover what you deposit, the LP tokens you get as a receipt, what your pool share actually means, and how trading fees quietly compound into your stake — plus the catch nobody mentions in the brochure.

Who fills the pool — and the both-tokens rule

A liquidity pool is just a smart contract holding reserves of two tokens. Traders shrink one reserve and grow the other every time they swap. To keep the party going, someone has to stock those reserves first. That someone is a liquidity provider, and joining has one firm rule: you deposit both tokens, in the pool’s current ratio.

Why both? Because a deposit must not move the price. The price is just the ratio of the two reserves (last lesson’s x·y=k world), so if you dumped in only ETH you’d skew the ratio and change the price — and the protocol won’t let a deposit masquerade as a trade. Matching the existing ratio adds to both reserves equally, leaving the price untouched.

Let’s make it concrete. Say the ETH/USDC pool currently holds:

The ratio is 1 ETH : 2000 USDC (so ETH is trading at $2000). You want to add $10000 of liquidity. You can’t just hand over $10000 of ETH — you split it down the middle of the value:

• Half the value in ETH: $5000 ÷ $2000 = 2.5 ETH
• Half the value in USDC: 5000 USDC

Deposit 2.5 ETH + 5000 USDC and you’ve added $10000 at exactly the pool’s ratio. The price doesn’t budge; the reserves just got a little deeper.

LP tokens: your receipt for the pool

When you deposit, the pool doesn’t write your name in a ledger. It mints you LP tokens — brand-new tokens that represent your stake in the pool. They’re a claim, not the assets themselves: holding LP tokens means “I own this fraction of whatever is in the pool,” and you redeem them by burning them to pull your share back out.

Think of it as a coat-check ticket. You hand over your coat (the two tokens) and get a numbered stub. The stub isn’t a coat — it’s a claim on a coat. Hand the stub back and you get your coat returned. LP tokens work the same way, with two twists: anyone holding the stub can redeem it (LP tokens are transferable, even tradeable), and the “coat” you get back is your share of the pool as it stands now, not the exact garments you checked in.

That last twist matters. Because the pool’s mix shifts as people trade, the tokens you withdraw won’t necessarily match what you put in — but the value of your claim tracks your share of the pool the whole time. More on that wrinkle at the end.

Pool share: what fraction of the pie you own

Your pool share is the fraction of the whole pool you own after you join:

$\text{share} = \frac{\text{your deposit value}}{\text{total pool value after you join}}$

Back to the numbers. Before you arrive, the pool is worth:

$100 \times 2000 + 200000 = 400000$

That’s $400000 in reserves. You add $10000, so the pool becomes worth $410000, and your slice is:

$\text{share} = \frac{10000}{410000} \approx 0.0244 = 2.44\%$

You’d be minted about 2.44% of the LP token supply. From now on, your LP tokens always entitle you to 2.44% of whatever the pool holds — which is the key to how you get paid.

How fees accrue to your share

Here’s the payoff. Every swap pays a 0.3% fee straight into the pool, so the reserves quietly grow over time. The number of LP tokens never changes from a swap — only the reserves they’re a claim on. So you own a fixed percentage of a slowly growing pie. Your share doesn’t go up; the pie it’s a slice of does.

Watch the worked numbers. Suppose this pool does $5000000 of trading volume per day:

• Daily fees into the pool: $5000000 × 0.3% = $15000/day
• Your cut at 2.44%: $15000 × 0.0244 ≈ $366/day
• Annualized: $366 × 365 ≈ $133000/year on a $10000 stake — if that volume holds every single day.

Try it yourself. Slide your deposit and watch your LP tokens, pool share, and projected fee earnings update in real time:

Two more details worth knowing:

• Fees auto-compound. They’re not paid out as a separate stream — they fold straight into the reserves, so your LP tokens slowly become redeemable for more than you deposited. You only realize the gains when you burn your LP tokens and withdraw.
• More LPs dilute your share. When other providers deposit, the pool grows but your slice shrinks. Say the pool doubles in size with newcomers: your 2.44% might fall toward 1.2%, so your cut of each fee halves. You’re not robbed — your LP tokens are still worth their full share — but your fee rate per dollar staked drops as the pool’s total value (TVL) rises. Deeper pools are safer for traders and stingier for any single LP.

Withdrawing — and the catch called impermanent loss

To cash out, you burn your LP tokens and the pool hands you back your current share of whatever the reserves are now. And “now” is the catch: the mix may have changed since you deposited.

Why? Arbitrage rebalances the pool. If ETH’s market price rose, traders bought ETH out of the pool until its in-pool price caught up — draining ETH, piling in USDC. Burn your LP tokens after that and you get back less ETH and more USDC than you put in (still worth your 2.44% share, just a different blend). If ETH fell, the reverse: more ETH, less USDC.

So you rarely withdraw the exact ratio you deposited — and here’s the sting: the value of that rebalanced bundle is usually a little less than if you’d just held the two tokens in your wallet. That gap is impermanent loss, and it’s the single most important risk an LP takes. It’s the whole of lesson 5, so we won’t compute it here — just plant the flag: fees pay you, impermanent loss can take some of it back.

Key Takeaways

Next up: slippage — why a big swap moves the pool along its curve and pays a worse average price than the quote you saw.