Users with a positive balance of the base asset earn interest, denominated in the base asset, based on a supply rate model; users with a negative balance pay interest based on a borrow rate model. These are separate interest rate models, and set by governance.
The supply and borrow interest rates are a function of the utilization rate of the base asset. Each model includes a utilization rate “kink” - above this point the interest rate increases more rapidly. Interest accrues every second using the block timestamp.
Collateral assets do not earn or pay interest.
This function returns the per second supply rate as the decimal representation of a percentage scaled up by 10 ^ 18. The formula for producing the supply rate is:
## If the Utilization is less than or equal to the Kink parameter
SupplyRate = supplyPerSecondInterestRateBase + supplyPerSecondInterestRateSlopeLow * utilization
## Else
SupplyRate = supplyPerSecondInterestRateBase + supplyPerSecondInterestRateSlopeLow * supplyKink + supplyPerSecondInterestRateSlopeHigh * (utilization - supplyKink)
To calculate the Compound III supply APR as a percentage, pass the current utilization to this function, and divide the result by 10 ^ 18 and multiply by the approximate number of seconds in one year and scale up by 100.
Seconds Per Year = 60 * 60 * 24 * 365
Utilization = getUtilization()
Supply Rate = getSupplyRate(Utilization)
Supply APR = Supply Rate / (10 ^ 18) * Seconds Per Year * 100
function getSupplyRate(uint utilization) public view returns (uint64)
utilization: The utilization at which to calculate the rate.RETURNS: The per second supply rate as the decimal representation of a percentage scaled up by 10 ^ 18. E.g. 317100000 indicates, roughly, a 1% APR.Comet comet = Comet(0xCometAddress);
uint supplyRate = comet.getSupplyRate(0.8e18);
const comet = new ethers.Contract(contractAddress, abiJson, provider);
const supplyRate = await comet.callStatic.getSupplyRate(0.8e18);
This function returns the per second borrow rate as the decimal representation of a percentage scaled up by 10 ^ 18. The formula for producing the borrow rate is:
## If the Utilization is less than or equal to the Kink parameter
BorrowRate = borrowPerSecondInterestRateBase + borrowPerSecondInterestRateSlopeLow * utilization
## Else
BorrowRate = borrowPerSecondInterestRateBase + borrowPerSecondInterestRateSlopeLow * borrowKink + borrowPerSecondInterestRateSlopeHigh * (utilization - borrowKink)
To calculate the Compound III borrow APR as a percentage, pass the current utilization to this function, and divide the result by 10 ^ 18 and multiply by the approximate number of seconds in one year and scale up by 100.
Seconds Per Year = 60 * 60 * 24 * 365
Utilization = getUtilization()
Borrow Rate = getBorrowRate(Utilization)
Borrow APR = Borrow Rate / (10 ^ 18) * Seconds Per Year * 100
function getBorrowRate(uint utilization) public view returns (uint64)
utilization: The utilization at which to calculate the rate.RETURNS: The per second borrow rate as the decimal representation of a percentage scaled up by 10 ^ 18. E.g. 317100000 indicates, roughly, a 1% APR.Comet comet = Comet(0xCometAddress);
uint borrowRate = comet.getBorrowRate(0.8e18);
const comet = new ethers.Contract(contractAddress, abiJson, provider);
const borrowRate = await comet.callStatic.getBorrowRate(0.8e18);
This function returns the current protocol utilization of the base asset. The formula for producing the utilization is:
Utilization = TotalBorrows / TotalSupply
function getUtilization() public view returns (uint)
RETURNS: The current protocol utilization percentage as a decimal, represented by an unsigned integer, scaled up by 10 ^ 18. E.g. 1e17 or 100000000000000000 is 10% utilization.Comet comet = Comet(0xCometAddress);
uint utilization = comet.getUtilization(); // example: 10000000000000000 (1%)
const comet = new ethers.Contract(contractAddress, abiJson, provider);
const utilization = await comet.callStatic.getUtilization();
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