Aave Interest Accrual Calculator

Aave hands you an interest-bearing token for every position: an aToken when you supply, a variable debt token when you borrow. These rebase, so the balance climbs continuously without any transaction. That is convenient to hold and awkward to account for, because the balance alone cannot tell you how much was deposited and how much is interest.

Every balance change does emit an event, though, and each one separates the principal moved from the interest applied. Summing the principal across a position's whole history gives the net principal, and the rest of the balance has to be interest:

Because supplies, withdrawals, borrows, repayments, aToken transfers, collateral swaps and liquidation seizures all emit one of these events, the identity is exact rather than an estimate. It holds for positions that have been topped up and drawn down dozens of times, which is where APY-based estimates fall apart.

Interest is credited to your balance whenever the position is touched. Anything credited by a past event is realized interest; whatever has built up since the most recent event is still pending. Both are real, and the two together are the position's lifetime interest.

The distinction matters for record-keeping. Realized interest is anchored to a block and a timestamp, so it can be tied to a date; pending interest is a live number that changes every block until the next interaction.

Aave's pools carry a per-second interest rate. The APR is that rate annualized without compounding, while the APY assumes every second's interest is left in place to earn more:

The gap widens as rates rise: a 5% APR compounds to about 5.13% APY, whereas a 40% APR reaches roughly 49%. Supply APYs are quoted net of the reserve factor, the share of borrower interest the protocol keeps, which is why suppliers always earn less than borrowers pay.

Both rates float with utilization — the fraction of the pool currently borrowed — so they can change block to block. A quoted APY is a snapshot, never a promise, and that is precisely why realized interest has to be reconstructed from events rather than projected from a rate.