APR and APY

You can query latest APR and APY on chain and subgraph

All rates queried on chain or subgraph, are expressed in RAY units i.e. 10^27. All emissions are expressed in WAD units i.e. 10^18.

APY: Compounding interest accrued by deposit or borrow on LendPool.

APR: Non Compounding rewards earned as part of LiquidityIncentives.

The deposit and borrow APR displayed on the BendDAO front-end is calculated in real-time when the lending pool utilization ratio is changed.

Conversions

Both of these conversions take the input and output in decimal form. Multiply the output by 100 to get the percentage.

APR -> APY

To convert the APR to APY compounded per second the formula is:

$$APY = (1 + (APR/secondsPerYear)) ^ {secondsPerYear} - 1$$

​APY -> APR

To convert the APY compounded per second to APR the formula is:

$$APR = ((1 + APY) ^ {1/secondsPerYear} - 1) * secondsPerYear$$

​Query Data

On-Chain

APR: using assets method to fetch liquidity mining incentives for bToken/debtToken.

APY: using getReserveData method to fetch deposit and borrow rates of assets.

// asset address is the ERC20 deposited or borrowed, eg. WETH, USDT

[, liquidityIndex, variableBorrowIndex, 
currentLiquidityRate, currentVariableBorrowRate, ,
bTokenAddress,
debtTokenAddress, , ] = LendPool.getReserveData(asset.address)

totalBTokenSupply = bTokenAddress.totalSupply()
totalCurrentVariableDebt = debtTokenAddress.totalSupply()

[bEmissionPerSecond,,] = IcentivesController.assets(bTokenAddress)
[dEmissionPerSecond,,] = IcentivesController.assets(debtTokenAddress)

Subgraph (GraphQL)

Use subgraph to query reserve data.

There's no public subgraph service now, you need to deploy it by yourself. Please try to query the data from the on-chain smart contracts.

{
  reserves {
    name
    underlyingAsset
    
    liquidityRate 
    variableBorrowRate
    
    totalBTokenSupply
    totalCurrentVariableDebt
  }
}

Compute Data

RAY = 10**27 // 10 to the power 27
SECONDS_PER_YEAR = 31536000
TOKEN_DECIMALS = 18 // same as the underlying asset, etc.18 for WETH, 6 for USDT
REWARD_DECIMALS = 18 // BEND token is 18 always
TOKEN_PRICE_ETH = ??? // using Chainlink contract to get the price, 1e18 for WETH
REWARD_PRICE_ETH = ??? // using Uniswap V2 BEND/ETH pair contract to calculate the price 

// Deposit and Borrow calculations for reserve (etc. WETH, USDT)
// APY and APR are returned here as decimals, multiply by 100 to get the percents

depositAPR = liquidityRate/RAY
variableBorrowAPR = variableBorrowRate/RAY

depositAPY = ((1 + (depositAPR / SECONDS_PER_YEAR)) ^ SECONDS_PER_YEAR) - 1
variableBorrowAPY = ((1 + (variableBorrowAPR / SECONDS_PER_YEAR)) ^ SECONDS_PER_YEAR) - 1

// Incentives calculations for BEND token

bEmissionPerYear = bEmissionPerSecond * SECONDS_PER_YEAR
dEmissionPerYear = dEmissionPerSecond * SECONDS_PER_YEAR

incentiveDepositAPRPercent = 100 * (bEmissionPerYear * REWARD_PRICE_ETH * TOKEN_DECIMALS)/
                          (totalBTokenSupply * TOKEN_PRICE_ETH * REWARD_DECIMALS)

incentiveBorrowAPRPercent = 100 * (dEmissionPerYear * REWARD_PRICE_ETH * TOKEN_DECIMALS)/
                          (totalCurrentVariableDebt * TOKEN_PRICE_ETH * REWARD_DECIMALS)