Divide the annual interest rate by 365 to calculate the daily interest rate for your loan. For example, a loan with a 10% annual interest rate would have a daily interest rate of 0.0273%. Convert that rate to a decimal (0.0273 / 100 = 0.000273) and multiply it by your remaining principal to see how much interest is accruing each day. If you had $10,000 in principal left on our example loan, you’d be charged roughly $2.73 per day in interest.