Interest Rate Model
The adaptive interest rate model in Tarot determines Borrow and Supply APRs for each lending pool. All lending pools are isolated, and each borrowable pool uses its own interest rate model that acts independently from all other borrowable pools.
Similar to protocols like Aave and Compound, Tarot uses a “kinked” interest rate model with a single adjustable parameter (kinkUtilizationRate, ranging from 70% to 90%) to be adjusted by governance.
Utilization rate is the percentage of tokens supplied by lenders to a lending pool that are currently utilized by borrowers in outstanding loans. Depending on the current utilization rate (utilizationRate) of a borrowable pool, the borrow rate (borrowRate) is determined by the following parameters:
  • utilizationRate = 0 implies borrowRate = 0;
  • utilizationRate = kinkUtilizationRate implies borrowRate = kinkBorrowRate;
  • utilizationRate = 100% implies borrowRate = 5 * kinkBorrowRate.
The kinkBorrowRate is updated between blocks on a per-second basis using the previous borrowRate for the borrowable pool. This ensures Borrow and Supply APRs are determined according to the supply and demand equilibrium for each lending pool.
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