Interpreting Exchange Rates

The aToken Exchange Rate is scaled by the difference in decimals between the aToken and the underlying asset.

const oneSTokenInUnderlying = exchangeRateCurrent / (1 * 10 ^ (18 + underlyingDecimals - aTokenDecimals))

Here is an example of finding the value of 1 cBAT in BAT with Web3.js JavaScript.

const aTokenDecimals = 8; // all aTokens have 8 decimal places
const underlying = new web3.eth.Contract(erc20Abi, batAddress);
const aToken = new web3.eth.Contract(aTokenAbi, sUsdcAddress);
const underlyingDecimals = await underlying.methods.decimals().call();
const exchangeRateCurrent = await aToken.methods.exchangeRateCurrent().call();
const mantissa = 18 + parseInt(underlyingDecimals) - aTokenDecimals;
const oneSTokenInUnderlying = exchangeRateCurrent / Math.pow(10, mantissa);
console.log('1 aUSDC can be redeemed for', oneSTokenInUnderlying, 'USDC');

There is no underlying contract for ETH, so to do this with aBNB, set underlyingDecimals to 18.

To find the number of underlying tokens that can be redeemed for aTokens, multiply the number of aTokens by the above value oneSTokenInUnderlying.

const underlyingTokens = aTokenAmount * oneSTokenInUnderlying