Interest mechanics
Student Loan Interest Explained
Most student loans use simple daily interest. Interest accrues on the outstanding principal each day, then payments generally cover charges and accrued interest before reducing principal.
The daily-interest formula
For a $37,000 balance at 5.8%, the estimate is:
Over 30 days that is roughly $176 before any principal reduction. Because the balance normally falls after a payment, the next period’s daily interest is calculated from a slightly smaller number.
Use the student loan interest calculator to estimate daily and monthly interest for your balance and rate.
Simple interest and capitalization are different
Accrued interest
Interest that has built up but has not been paid. On a simple-interest loan, new interest is ordinarily calculated from principal, not from this separate accrued amount.
Capitalized interest
Unpaid interest that is added to principal after a qualifying event. Once added, it becomes part of the balance used to calculate later interest.
Capitalization can make the balance grow even if you did not borrow more. Federal rules governing when capitalization occurs have changed over time and differ from private-loan contracts, so verify the rule that applies to your loan at Federal Student Aid or with your servicer.
How a payment reaches principal
A common payment sequence is charges or fees first, then accrued interest, then principal. The exact order is controlled by the promissory note, program rules and servicer procedures.
Applicable amounts are handled first.
Interest since the last payment is covered.
The remainder lowers the balance.
This explains why the principal drop can be smaller than the payment. It does not mean the payment failed; part of it covered the cost that had already accrued.
What extra principal changes
Extra principal lowers the balance used for future interest calculations. If the required payment stays the same, more of later payments can reach principal and the loan can finish earlier. Run the full schedule in the student loan payoff calculator.
It can change
Total interest, payoff date, remaining balance and the interest share of future payments.
It usually does not change
The contractual interest rate or required monthly payment unless the loan is refinanced, recast or otherwise modified.
Tell the servicer where to apply extra money and verify the next statement. A “paid ahead” status is not the same as a principal-only instruction.
Why your statement may differ from a calculator
- The number of days between payment dates changes the accrued interest.
- Servicers can use specific rounding and day-count rules.
- Variable rates can change during the payoff period.
- Fees, late payments, deferment, forbearance or capitalization can alter the balance.
- Payments may be allocated across several loan groups using instructions you selected or default rules.
Our calculators use monthly amortization for planning consistency. See our methodology for assumptions and use the servicer’s official payoff quote for an exact payoff transaction.
Sources
- Federal Student AidUnderstand How Interest Is Calculated and What Fees Are Associated With Your Federal Student Loan
- Federal Student AidRepaying Your Loans
- Consumer Financial Protection BureauHow does paying down a student loan work?
Estimate interest on your balance
Enter your current balance and APR to see the estimated daily, monthly and yearly interest.
Open the interest calculatorEducational content, not financial, tax or legal advice. Calculations are estimates; your promissory note, servicer records and current program rules control actual interest, capitalization and payment application.