Cumulative interest is when the interest over one period (say one month) gets reinvested the next month to earn even more interest. Savings accounts that generate compound interest normally express their rate as an Annual Percentage Yield (APY) which includes the compounding affect of these interest payments to determine a total income rate for the year. It is worth paying attention the interest calculation and payment frequency of different platforms. Some platforms will calculate and pay out interest daily. Others calculate interest daily but pay out monthly. In some cases the interest calculated daily is still compounded daily even though it is actually paid out monthly.