How the instalment is calculated
New rules (EIR): a standard reducing-balance instalment, M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where r is the monthly effective rate and n the number of months.
Old flat rate: total interest = loan amount × flat rate × years. Add that to the loan and divide by the months. The calculator also shows the effective rate a flat-rate loan really costs, so you can compare the two offers.