This is an approximation only based on 360 days. Our calculation is an approximation based on simple interest. For example, if you provide $ 10 for $9000 (deposit) for 30 days, the percentage % Per Annum (%PA) is 10/9000 = 0.00111 for 30 days or 0.000037 per day, times 360 days = 1.33% PA. We merely annualised the interest amount to % PA so that it has some resemblance to what most people are comfortable with. The fact is that the amount of interest should be the amount you receive at the end of the deposit period and that is the amount billed to your banker. We used 360 days as this is a conservative %. There is no compound calculation here, what you ask is what you receive. If it is compounded then the % is higher but not all banks will do this and is up to you whether you want to reinvest the interest so we think is better to erred on the conservative side.