The lend APR is calculated based on the past lending gains and the assured future repayments of the current set of loans on a per currency level. The past lending gains are taken into consideration because of the future loans that will be taken and repaid(with interest) in the next few days. This is the formula for calculating the lending APR.

lend APR for a currency = (recent_past_annualised_rate + mid_term_future_annualised_rate) / 2

recent_past_annualised_rate for a currency = For i in last 30 days, Sum(interest paid in given currency on day i / active reserve volume of given currency on day i)

mid_term_future_annualised_rate for a currency = For i in next 90 days, Sum(interest expected in given currency due to already active loan’s tenure completion on day i / current active reserve volume of given currency)