DeFi lending and borrowing refers to protocols that let users deposit crypto assets to earn interest, or lock up collateral to take out loans — all without a bank, credit check, or human intermediary. The entire process runs on smart contracts, making it transparent, non-custodial, and available to anyone with an internet connection.
This sounds almost too convenient. Understanding how it actually works — and where it can go badly wrong — is essential before you interact with any of these protocols.
How traditional lending differs from DeFi lending
In a traditional bank, deposits are pooled and loaned out to vetted borrowers. The bank earns the spread between deposit interest and loan interest, absorbs default risk through insurance schemes, and decides who gets credit.
DeFi lending protocols replace this entire infrastructure with code. There are no credit scores, no identity checks, and no negotiation. The protocol’s rules are public, and the same rules apply to every participant, automatically.
The trade-off is that because the protocol cannot assess your creditworthiness or pursue you in court if you default, it requires you to put up more collateral than you borrow. This is called overcollateralization.
Supplying assets to earn interest
When you deposit tokens into a lending protocol, you are adding to a shared pool. Borrowers draw from that pool and pay interest. That interest flows back to depositors in proportion to their share of the pool.
Interest rates in most protocols are not fixed — they adjust algorithmically based on utilization rate: how much of the deposited pool is currently being borrowed. If utilization is low (few borrowers), rates drop to attract borrowers. If utilization is high (nearly all funds are borrowed), rates rise to attract more depositors and discourage further borrowing.
A high utilization rate also means depositors face liquidity risk: if most of the pool is out on loan, you may not be able to withdraw your full deposit immediately. Well-designed protocols reserve a portion of the pool to prevent this, but extreme conditions can make withdrawals temporarily impossible.
When you deposit, you typically receive a receipt token representing your share of the pool. On Aave, for example, depositing ETH gives you aETH. These receipt tokens accrue interest automatically and can sometimes be used in other DeFi protocols.
Borrowing: collateral and health factors
To borrow from a DeFi protocol, you first deposit collateral. The protocol then allows you to borrow a fraction of that collateral’s value in another asset.
The ratio of how much you can borrow relative to your collateral is called the loan-to-value (LTV) ratio. For example, if a protocol allows 75% LTV on ETH, depositing 1,000 USD worth of ETH lets you borrow up to 750 USD worth of another token.
Why would someone borrow like this? Common reasons include:
- Accessing liquidity without selling an asset (and triggering a taxable event)
- Borrowing stablecoins to deploy elsewhere
- Leveraged positions (borrowing to buy more of an asset — high risk)
Protocols track each borrower’s health factor — a real-time measure of how safely collateralized the position is. A health factor above 1 means the position is in good standing. As collateral prices fall or borrowed asset prices rise, the health factor drops.
| Health factor | Status |
|---|---|
| Above 1.0 | Safe — collateral covers the loan |
| Approaching 1.0 | At risk — consider adding collateral or repaying |
| Below 1.0 | Liquidation triggered |
Liquidations: what happens when collateral falls
Liquidation is the mechanism that keeps lending protocols solvent. If a borrower’s collateral value drops enough that it no longer adequately covers the loan, the protocol allows third-party liquidators to repay part of the debt and claim the collateral at a discount.
Here is the sequence:
- Prices move against the borrower (e.g., deposited ETH drops in value)
- Health factor falls below the threshold
- A liquidator repays a portion of the borrower’s debt
- The liquidator receives the equivalent value of collateral, plus a liquidation bonus (often 5–10%)
- The borrower loses that portion of their collateral
Liquidators are generally bots that monitor protocol health factors continuously and compete to execute profitable liquidations the moment a position crosses the threshold. From the protocol’s perspective, this is a feature: it outsources enforcement to market participants who have financial incentive to act quickly.
From a borrower’s perspective, liquidation means losing part of your collateral to pay back a loan you still had the assets to repay — just not enough buffer to survive a price drop. This is why maintaining a comfortable health factor, not borrowing at maximum LTV, is critical.
Flash loans: borrowing without collateral
A uniquely DeFi concept is the flash loan — an uncollateralized loan that is borrowed and repaid within a single blockchain transaction. If the full repayment does not happen in the same transaction, the entire transaction reverts as if it never occurred.
Flash loans are not for everyday users — they require programming. They are used for things like arbitrage between exchanges, collateral swaps, and liquidations themselves. They cannot be used to “steal” money in the normal sense because the blockchain enforces atomic repayment. However, they have been used as components in complex attacks against poorly designed protocols.
Risk factors every user should understand
DeFi lending introduces several risks beyond ordinary market volatility:
Smart contract risk. Protocols can contain bugs. Even audited contracts have been exploited. Funds deposited in a protocol are only as safe as the code. Understanding the basics of how smart contracts work helps contextualize this.
Oracle risk. Protocols need accurate price data to calculate health factors. They rely on oracles to feed prices on-chain. If an oracle is manipulated, a protocol can be tricked into mispricing collateral.
Governance risk. Many protocols are controlled by governance token holders who can vote to change parameters — including LTV ratios, supported collateral types, and interest rate models. See how governance and DAOs work for context.
Liquidity risk. As noted above, high utilization can temporarily prevent withdrawals.
These risks do not mean lending protocols are unusable — many have operated for years with large sums — but they are real and deserve weight in any decision.
Key takeaways
- DeFi lending replaces banks with smart contracts: deposits earn interest from a shared pool, and borrowing requires overcollateralized collateral.
- Interest rates adjust algorithmically based on how much of the pool is currently in use.
- Your health factor measures the safety of your position; falling below the liquidation threshold triggers automatic collateral seizure by third-party liquidators.
- Flash loans are uncollateralized loans that must be repaid in the same transaction — a primitive used by developers, not typical users.
- Smart contract bugs, oracle manipulation, and governance decisions are risks that market volatility alone does not capture.
- Never borrow at maximum LTV; maintain a cushion so that normal price swings do not trigger liquidation.
Next up: Impermanent Loss