Lending and borrowing in DeFi replaces the bank with a smart contract. Protocols like Aave and Compound let anyone earn interest on deposits or take out loans — no credit check, no application, no banker. Billions of dollars flow through these money markets daily. Here’s how they work under the hood, and the risks to respect. Note: crypto markets are volatile; this is educational, not financial advice.
Lending and Borrowing in DeFi: How the Pool Model Works
Unlike peer-to-peer lending, Aave and Compound use liquidity pools. Lenders deposit assets (ETH, USDC, wBTC, and others) into a shared pool and immediately start earning interest. Borrowers draw from the same pool, paying interest that flows back to lenders. A smart contract — not a loan officer — manages every deposit, withdrawal, and repayment around the clock.
Your deposit is represented by interest-bearing tokens (aTokens on Aave, cTokens on Compound) that grow in value or quantity as interest accrues, so you can watch earnings accumulate in real time.
Overcollateralization: The Core Safety Rule
Because DeFi has no credit scores or legal recourse, loans must be overcollateralized: you lock up more value than you borrow. Typical parameters:
- Loan-to-value (LTV): e.g., 75% — deposit $10,000 of ETH to borrow up to $7,500.
- Liquidation threshold: if your collateral’s value falls near the loan value, anyone can repay part of your loan and claim your collateral at a discount.
- Health factor: Aave’s single number summarizing your position’s safety — keep it comfortably above 1.
Liquidation is automatic and unsentimental. A sharp market drop can liquidate positions in minutes, which is why conservative borrowers keep health factors high.
How Interest Rates Are Set
Rates are algorithmic, driven by utilization — the share of the pool currently borrowed:
- Low utilization → low borrow rates (to attract borrowers) and low supply APYs.
- High utilization → rates spike, attracting new lenders and encouraging repayments.
- Near 100% utilization → rates can skyrocket, and withdrawals may temporarily fail until liquidity returns.
Aave offers both variable rates (which move with utilization) and stable rates (fixed short-term, rebalanced by governance in extreme conditions). Compound’s v3 (Comet) streamlined the design around single borrowable assets per market for capital efficiency.
Aave vs Compound: Key Differences
- Asset breadth: Aave supports a wider range of collateral and borrow assets across many networks; Compound v3 focuses on fewer, high-quality assets per deployment.
- Features: Aave pioneered flash loans, credit delegation, and features like isolation mode and efficiency mode (eMode) for correlated assets.
- Risk framework: both use governance-set risk parameters and risk-service providers, but their market structures and liquidation engines differ in detail.
- Track record: both are battle-tested across multiple market cycles — a key reason they dominate DeFi lending.
Common Strategies (and Their Risks)
- Earning supply yield: deposit stablecoins or ETH to earn interest — the simplest, lowest-risk use.
- Borrowing for leverage: borrow against ETH to buy more crypto — amplifies gains and liquidation risk alike.
- Recursive looping: deposit, borrow, redeposit repeatedly to stack yields — profitable in calm markets, dangerous in volatile ones.
- Shorting: borrow an asset you expect to fall, sell it, buy back cheaper later — timing risk plus borrow costs.
Risks of DeFi Lending
- Liquidation cascades: volatile markets can liquidate your position faster than you can react — use alerts and conservative LTVs.
- Smart contract risk: even audited protocols can harbor bugs; both Aave and Compound have strong records, but no code is provably safe.
- Oracle risk: liquidations depend on price feeds; oracle manipulation or failures can cause wrongful liquidations.
- Governance risk: token-holder votes can change parameters, add or freeze assets.
- Stablecoin depeg: borrowing or supplying a stablecoin that depegs breaks the assumptions your position was built on.
Aave’s Risk Controls: Isolation Mode and eMode
Aave layers extra risk tooling on top of the basics:
- Isolation mode: newly listed or riskier assets can only be used as collateral in isolation — you can borrow only approved stablecoins against them, and can’t combine them with other collateral. This quarantines contagion if the asset collapses.
- Efficiency mode (eMode): for highly correlated assets (like ETH and stETH), eMode raises LTV limits, recognizing that correlated collateral is safer to borrow against. It’s what makes leveraged staking loops capital-efficient.
- Supply and borrow caps: governance sets per-asset ceilings so no single asset can dominate a market.
- Freezes and pauses: in emergencies, governance can freeze new activity on an asset without trapping existing users.
These controls are part of why Aave has survived volatile markets — but they’re guardrails, not guarantees. Your health factor is still your responsibility.
Getting Started Safely
- Use the official Aave or Compound app (bookmark it; phishing copies are common).
- Start with a small supply deposit to learn the mechanics.
- If borrowing, keep your health factor well above the minimum and set price alerts.
- Understand every token you approve, and revoke unused approvals.
- Prefer established markets and avoid exotic collateral until you’re experienced.
DeFi lending turned idle crypto into productive capital and created borrowing without banks. Used conservatively — modest leverage, quality collateral, constant monitoring — it’s one of DeFi’s most genuinely useful primitives.
