Interest rates for Stafford and PLUS Loans are established each year on July 1 based on the most recent 91-Day Treasury Bill auction in May, plus a margin determined by the U.S. Department of Education.

The formula to calculate accrued daily interest is:
Principal Balance * Interest Rate / 365.25 = Daily Accrued Interest
An example of how to calculate daily accrued interest is below.

For the purposes of this example, we are using $10,000 as the principal balance with a 5% interest rate.

10,000 * 5% = 500 (Principal balance multiplied by the interest rate)
500 / 365.25 = 1.36, which is the daily accrued interest. (Sum of the principal balance multiplied by the interest rate (500) divided by 365.25)