Aave Interest Rate Model: DeFi Dynamic Rate Engine

Frequently Asked Questions

01.What is RAY precision in Aave and why does it matter?

RAY precision is a 27-decimal fixed-point format (1e27) Aave uses for all interest rate calculations. It eliminates rounding errors that would accumulate in high-frequency compound interest math across millions of positions. Any integration that passes non-RAY values into Aave rate functions will silently produce incorrect borrow and supply rates.

02.How does Aave's two-slope kinked interest rate model work?

Aave applies a gentle slope (Slope1) when utilization is below the optimal target. Once utilization crosses that threshold, a steep Slope2 kicks in to sharply raise borrow costs, discouraging further draws and protecting depositor liquidity. The kink point is the boundary between these two regimes. (Aave V3 Risk Parameters, July 2025)

03.What is the Aave reserve factor and how does it affect supply rates?

The reserve factor is the share of gross borrow interest Aave routes to its DAO treasury instead of distributing to depositors. Typical values are in the ten-to-twenty-five percent range depending on asset risk. A higher reserve factor reduces the supply rate while keeping the borrow rate unchanged, widening the spread between what borrowers pay and what lenders earn.

04.How do you test Aave interest rate calculations with Foundry?

Fork mainnet at a specific block using vm.createFork, then call the deployed DefaultReserveInterestRateStrategy directly with controlled totalBorrowed and totalAvailable inputs. Assert that your local implementation matches Aave's on-chain output to within 1 RAY unit (1e0 tolerance). Use forge coverage to confirm all three utilization regimes are exercised: below optimal, at optimal, and above optimal.

05.What are the most common integration mistakes when implementing Aave rate math?

The three most common mistakes are: passing percentage values as plain integers instead of converting them to RAY format first, using integer division before RAY multiplication which floors precision early, and ignoring the reserve factor when estimating net supply yield for depositors. Each mistake produces an incorrect rate silently with no revert.