Crypto lending protocols allow users to deposit assets as collateral and borrow other assets against them, or supply assets to earn interest from borrowers. No credit check, no KYC on most protocols, no fixed terms, interest rates adjust automatically based on the ratio of supplied to borrowed capital in each pool.
How on-chain lending actually works
The dominant model is overcollateralized lending: you supply collateral worth more than what you borrow. Aave v3 allows borrowing up to 80% of your ETH collateral value (80% LTV). If you deposit $10,000 in ETH, you can borrow up to $8,000 USDC. The protocol charges variable or stable interest on the borrow and pays variable interest to suppliers. Interest accrues per block, not daily, so rates displayed as annual APR compound continuously in practice.
Utilization rate drives interest rates through an algorithmic curve. When 90% of a pool’s supply is borrowed, the borrow rate spikes sharply (the “kink” in the interest rate model) to incentivize new suppliers and discourage new borrowers. Aave’s USDC borrow rate at 80% utilization is roughly 5–8%; at 95% utilization it can hit 50%+ annualized. This automatic adjustment is what makes the protocol functional without a central counterparty. Compound pioneered this model; Aave, Morpho Blue, and Euler have iterated on it with isolated markets, capital efficiency improvements, and more granular risk management. The liquidation mechanism connects directly to oracle pricing, see our price oracle explainer for how protocol collateral values are determined and where oracle manipulation risk enters.
What this means for traders
Borrowing against crypto to buy more crypto (leverage without selling) is the primary use case. If you hold ETH long-term and expect it to appreciate, borrowing USDC against it lets you deploy that capital into yield strategies or further ETH purchases without triggering a taxable disposal in most jurisdictions. The cost is the borrow APR, sustainable when yield on the borrowed capital exceeds the borrow rate, unsustainable when it doesn’t.
Liquidation is the critical risk to model. When your collateral value falls toward the liquidation threshold (typically 82.5–85% LTV on Aave for ETH), bots automatically repay part of your debt and claim your collateral at a 5–10% discount. A 20% ETH price drop on an 80% LTV position is enough to trigger partial liquidation. In fast markets (March 2020, May 2021, November 2022), liquidations cascade: protocol liquidations push collateral prices down further, triggering more liquidations. During the LUNA collapse in May 2022, Aave’s ETH markets processed over $500M in liquidations in 48 hours without bad debt because collateral values dropped within the liquidation safety band. The Venus Protocol on BSC was less fortunate, a price oracle manipulation caused $200M in bad debt in 2021. For the full risk checklist, see our DeFi protocol risk guide.
A concrete example
You supply 5 ETH ($15,000 at $3,000/ETH) on Aave v3. Borrowing capacity at 80% LTV: $12,000 USDC. You borrow $8,000 USDC (53% LTV, giving you headroom). Borrow APR: 6%. You deploy the $8,000 USDC into a stablecoin yield strategy earning 8%. Net carry: +2% on $8,000 = +$160/year. But ETH drops 30% to $2,100. Your collateral is now worth $10,500; your borrow is still $8,000. LTV: 76%, approaching Aave’s 82.5% liquidation threshold. You either add collateral, repay some debt, or get liquidated. If ETH drops another 8% to $1,932, liquidation triggers. The liquidator repays $4,000 of your debt and claims $4,400 in ETH (10% discount). You lose the ETH, keep the remaining collateral, and still owe $4,000.
Frequently asked questions
Can you borrow without collateral in DeFi? Flash loans allow uncollateralized borrowing within a single transaction, the loan is issued and must be repaid before the transaction closes, or the whole thing reverts. This is used for arbitrage and liquidations by bots but is not useful for simple capital access. Undercollateralized loans (borrowing more than your collateral value) exist through protocols like Maple Finance and TrueFi, which rely on off-chain credit assessment of institutional borrowers, a fundamentally different model.
What happens to borrowed funds if a protocol gets hacked? If the lending pool contract is exploited and funds are drained, suppliers absorb the loss, the protocol cannot repay depositors from emptied reserves. Some protocols have safety modules (Aave has an AAVE staking module that can be slashed to cover shortfalls), but these cover only a fraction of potential losses. This is why supply-side users face smart contract risk even when not borrowing.
What is the difference between Aave and Morpho? Morpho Blue is a minimal, permissionless lending protocol where anyone can create a market for any collateral/borrow pair. Unlike Aave’s pooled model where all suppliers share risk, Morpho isolates each market, so exposure to a bad collateral asset does not spread to unrelated pools. The tradeoff is that isolated markets have less liquidity by default and require more active curation.
