Flash Loan

A flash loan is an uncollateralized loan that must be borrowed and repaid within a single blockchain transaction. If the loan is not repaid by the end of the transaction, the entire transaction reverts as if nothing happened — making default impossible.

By Crypto University EditorialLast updated May 27, 2026

ArbitrageDeFiSmart Contract

✦ Key Insight

Flash loans give any trader temporary access to enormous capital with no upfront collateral. They are used for legitimate arbitrage, collateral swaps, and self-liquidations, but also feature in many of the largest DeFi exploits, where attackers use them to move markets briefly.

✕ Common Misconceptions

Underestimating MEV searchers competing for the same arbitrage opportunities.

Forgetting that gas costs and fees can wipe out thin spreads.

Building strategies that work in simulation but fail in real execution due to slippage.

Detailed Explanation

How It Works: The borrower calls a flash loan contract, receives the funds, performs a sequence of operations (arbitrage, refinancing, etc.), and pays back the principal plus a small fee — all in one atomic transaction. The lender's funds either return with a fee or never leave because the transaction reverts.

FAQs:

Is taking a flash loan risky? Risk is mostly in the strategy, not the loan itself; failure just reverts the transaction at a gas cost.
Do I need to code? For practical use, yes — flash loans require building a contract that executes the full strategy atomically.

In Practice

“A trader borrows 10,000 ETH for one transaction, arbitrages a price difference between two DEXes, repays the 10,000 ETH plus a 0.05% fee, and keeps the difference — all without ever owning the ETH outside that block.”

Dig Deeper

Smart Contract

A smart contract is self-executing code stored on a blockchain that automatically performs actions when certain conditions are met.

DeFi

Short for “Decentralized Finance,” it refers to financial applications built on blockchain networks that operate without traditional intermediaries.

Arbitrage

Arbitrage is a trading strategy where a trader buys the same crypto asset on one exchange at a lower price and sells it on another exchange at a higher price. The goal is to profit from the temporary price difference between markets.

Get a $100K funded account

See current qualification terms and payout conditions.

View Offer