How much does an Aave flash loan cost?

Aave V3 charges a flash loan premium of 0.05% of the borrowed amount, so a 100,000 USD loan costs 50 USD in protocol fees. The full borrow plus the fee must be repaid in the same transaction or it reverts.

Are any flash loans free?

dYdX and Balancer V2 charge a 0% flash loan fee, so you pay only gas. Aave V3 charges 0.05% and Uniswap V3 flash swaps charge the pool fee tier, commonly 0.30%, so the cheapest venue depends on your route.

What is the break-even spread?

It is the arbitrage edge, as a percentage of the borrowed notional, needed just to cover the protocol fee plus gas. If your expected price spread is below this figure, the trade loses money even before slippage.

What happens if the trade is not profitable?

Flash loans are atomic: if the contract cannot repay the borrow plus fee at the end of the transaction, the whole transaction reverts and no loan is taken. You still pay gas for the failed attempt, which the tool lets you factor in.

Do these fee rates ever change?

Yes. Flash loan premiums are protocol parameters that governance can adjust, and Uniswap flash costs depend on the specific pool fee tier you route through. Always confirm the live rate before deploying capital.

DeFi Flash Loan Cost Calculator

Flash loans let you borrow large amounts with no collateral, provided you repay within the same transaction. The catch is the fee plus gas, which sets a hard floor on how thin an arbitrage can be. This calculator shows the fee, the total repayment, and the exact spread you need to break even.

How it works

The protocol charges a fixed premium on the borrowed amount:

fee            = amount × rate
total repayment = amount + fee
total cost      = fee + gas
break-even %    = total cost / amount × 100
net profit      = amount × (target spread % / 100) − total cost

Rates used are the protocol defaults: Aave V3 at 0.05%, dYdX and Balancer V2 at 0%, and Uniswap V3 flash swaps at the 0.30% pool fee tier. Because the entire borrow plus fee must be repaid atomically, an unprofitable trade simply reverts and you only pay gas.

Example

Borrowing 100,000 USD on Aave V3 costs 100000 × 0.0005 = 50 USD in fees. Add 40 USD of gas and the total cost is 90 USD, so the break-even arbitrage spread is 90 / 100000 × 100 = 0.09%. A target spread of 0.5% yields 100000 × 0.005 − 90 = 410 USD net.

Tips and notes

Always add slippage and price impact on top of the break-even figure — real fills move the pool. Fee rates are governance parameters and Uniswap costs depend on the pool tier you route through, so confirm live values before sending the transaction.