What Is a Flash Loan?
A flash loan is crypto borrowed and repaid in one blockchain transaction; if repayment fails, the whole transaction is reversed. It needs a smart contract.
Vahe HakobyanEditor-in-chief
Updated Oct 6, 20263 min readFact-checked
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Flash loans exist only in decentralized finance. A smart contract borrows from a lending pool, uses the money for one set of instructions, and repays before the transaction closes. That lets someone borrow a large amount for a moment, but the loan is a tool for code, not cash you can hold.
What Is a Flash Loan?
A flash loan is a loan with no collateral. The borrower and the lender are usually smart contracts. The same transaction must include the borrowing, the use of the funds, and the repayment. If any part fails, the blockchain reverses the entire transaction, so no loan exists. The lender does not need to seize collateral.
How Does a Flash Loan Work?
You need a smart contract to take a flash loan. Beginners usually need developer tools or a service that writes the contract for them. You cannot just open a lending app and hold the funds. The contract calls the lending pool, gets the funds, runs your instructions, and repays the pool plus its fee in the same transaction. If it cannot repay, the network treats the whole call as failed.
What Are Flash Loans Used For?
Flash loans power a few common moves in decentralized finance. Each ends with repayment in the same transaction. They are not only for attackers.
- Arbitrage: a contract buys a token on one exchange and sells it on another for more.
- Liquidations: a contract repays a borrower's debt and receives the collateral at a discount.
- Collateral swaps: a contract moves debt from one asset to another without closing the position first.
What Risks and Limits Exist?
A flash loan is not free money. A failed transaction still uses network resources and can cost fees, even though the loan is canceled. The main risks come from the code and the prices the transaction touches.
Frequently asked questions
There is no US law that bans flash loans by name. They still have to follow rules against fraud and market manipulation, and securities or commodities laws can apply.
The IRS treats crypto as property. Profit from a successful flash loan is generally taxable, and the lender fee can count as a cost. A reversed loan creates no gain.
They exist on smart-contract blockchains, with Ethereum as a common example. The exact protocols change, so check a protocol's documentation.
No. A regular crypto loan usually requires collateral and can stay open for days or longer. A flash loan has no collateral and must be repaid in the same transaction or it is canceled.
