Exchange Rate

Each bToken is convertible into an ever increasing quantity of the underlying asset, as interest accrues in the market. The exchange rate between a bToken and the underlying asset is equal to:

exchangeRate = (getCash() + totalBorrows() - totalReserves()) / totalSupply()

BErc20 / CEther

function exchangeRateCurrent() returns (uint)

• RETURN: The current exchange rate as an unsigned integer, scaled by 1e18.

Solidity

BErc20 bToken = BToken(0x3FDA...);
uint exchangeRateMantissa = bToken.exchangeRateCurrent();

Web3 1.0

const bToken = CEther.at(0x3FDB...);
const exchangeRate = (await bToken.methods.exchangeRateCurrent().call()) / 1e18;

Tip: note the use of call vs. send to invoke the function from off-chain without incurring gas costs.