Crypto Lending and Borrowing

One of DeFi's most useful primitives is collateralised lending: deposit an asset you want to hold long-term, borrow a stablecoin against it, and use that liquidity without selling your underlying position. A Bitcoin holder who is bullish long-term but needs $50,000 for a business investment doesn't have to sell Bitcoin — they can deposit BTC as collateral, borrow USDC, use the funds, and repay the loan to retrieve their Bitcoin. If Bitcoin's price rises during the loan period, they've retained full upside. This use case — accessing liquidity without triggering a taxable event or sacrificing position — is genuinely valuable.

How DeFi Lending Protocols Work

Protocols like Aave and Compound aggregate deposits into lending pools. Borrowers draw from these pools by depositing collateral worth more than the loan (over-collateralised). Interest rates adjust algorithmically based on pool utilisation — as more borrowers use a pool, the utilisation rate rises and so does the borrow rate, incentivising new depositors and discouraging marginal borrowers. When utilisation falls, rates drop to attract more borrowing.

Interest accrues continuously by the block. Lenders receive interest-bearing tokens (aTokens on Aave, cTokens on Compound) that automatically appreciate in value as interest accrues — no claiming required.

Collateralisation Ratios and Health Factor

Every borrowable asset has a Loan-to-Value (LTV) ratio — the maximum percentage of collateral value you can borrow. Ethereum on Aave has an LTV of ~80%, meaning you can borrow up to $800 USDC for every $1,000 of ETH collateral. Lower LTV ratios apply to more volatile or less liquid collateral.

Your health factor tracks the ratio of collateral value to borrowed value adjusted for liquidation thresholds. A health factor above 1.0 means the position is safe. When price movements push health factor below 1.0, the position becomes eligible for liquidation — bots immediately repay a portion of your debt and seize your collateral (plus a liquidation bonus) to restore the health factor.

To manage liquidation risk: borrow conservatively (target 50% LTV or lower, not the maximum), monitor collateral price actively, and maintain a stablecoin reserve to repay part of the debt if needed to restore health factor.

Use Cases for Borrowing

• Liquidity without selling: Access cash without triggering a taxable event or surrendering a long-term position. Applicable when you're confident in the long-term price of the collateral but need short-term liquidity.
• Leveraged long: Deposit ETH, borrow USDC, buy more ETH. This creates a levered ETH position — gains are amplified, losses are amplified, and liquidation becomes a risk if ETH falls significantly. Effectively a leveraged position without using the perpetual market.
• Yield strategies (looping): Deposit a yield-bearing asset as collateral, borrow the base asset, re-deposit to earn more yield. This "looping" amplifies yield but also amplifies liquidation risk and protocol exposure.
• Shorting: Borrow an asset you expect to decline, sell it at current prices, and repurchase later at a lower price to repay. This is native short-selling in DeFi without using futures.

CeFi Lending: Higher Yield, Counterparty Risk

Centralised crypto lending platforms (BlockFi, Celsius, Nexo historically; today primarily institutional-focused platforms remain after the 2022 CeFi collapses) offered higher interest rates on deposits than DeFi but required trusting the platform with custody of assets. The 2022 collapse of Celsius and BlockFi demonstrated the catastrophic counterparty risk inherent in CeFi lending — billions in depositor funds were lost when these platforms became insolvent. Current retail CeFi lending options should be evaluated with extreme caution. The DeFi alternatives (Aave, Compound, MorphoBlue) carry smart contract risk but eliminate counterparty insolvency risk.

Flash Loans: A Unique DeFi Primitive

Flash loans are loans that must be borrowed and repaid within a single blockchain transaction. No collateral is required — the protocol relies on transaction atomicity: if the loan isn't repaid in the same transaction, the entire transaction reverts as if it never happened. Flash loans enable capital-efficient arbitrage, self-liquidation (repaying a DeFi loan with borrowed funds to avoid a worse liquidation), and have famously been used in oracle manipulation attacks. They are available on Aave at 0.09% fee.

Summary

Crypto lending lets you earn interest on deposits; borrowing against collateral provides liquidity without selling. DeFi protocols (Aave, Compound) use algorithmic rates and over-collateralisation enforced by liquidation bots. Monitor your health factor — when it falls below 1.0, liquidation occurs at a penalty. Borrow conservatively (50% LTV target), maintain a repayment reserve, and use DeFi over CeFi to eliminate counterparty insolvency risk. The primary use cases are liquidity access without selling, leveraged longs, and short selling without using perps.