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Step 1
Find the daily interest rate on the CD. The base rate a CD pays is the annual percentage of the principal amount of the CD a bank or credit union pays you for the use of your money. The daily interest rate is equal to the base rate divided by 365 (the number of days in a year). For example, if the base rate is 4.38 percent per year, the daily interest rate is 4.38 percent divided by 365 or 0.012 percent.
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Step 2
Calculate interest for a single day. Multiply the balance in the CD by the daily interest rate. If you have a $10,000 CD with a daily interest rate of 0.012 percent, that's $10,000 times 0.012 percent. In this example the day's interest is $1.20, which you add to the balance of the CD for an ending balance of $10,001.20.
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Step 3
Understand how compounded daily interest on a CD works. As soon as each day's interest is added to the CD, the additional money starts earning more interest. As a result, calculate each day's interest and use that day's ending balance for the following day's interest calculation.
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Step 4
Use a formula to calculate daily interest on a CD for any number of days. For daily interest, the formula is T = B times (1 + r/365)^d -- B. T is the total interest earned and B is your starting balance. The "r" stands for the annual interest rate. The ^d symbol indicates that d (the number of days) is an exponent. Enter the data in your calculator or software according to its instructions. For the example used in Steps 1 and 2, the formula for 30 days interest would look like this: T =$10,000 times (1 + 0.048/365)^30 - $10,000.
