Student Loan Interest Calculator
See how much of your payment goes to interest vs principal each month.
By Konstantin Iakovlev · Updated September 2026 · Source: Federal Student Aid — Federal interest rates and fees
Daily Interest
$5.27
Payoff Time
9.4 years
Total Interest
$9,835.30
Payment Allocation
| Monthly Interest | $160.42 |
| To Principal | $239.58 |
| % Going to Interest | 40.1% |
| Payoff Date | 113 months (9.4 yrs) |
Use the Student Loan Interest Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.
How It Works
Every loan payment you make splits in two: part covers interest, part chips away at principal. Seeing that division clearly is the foundation of any repayment strategy and a realistic budget. Watching the breakdown month by month reveals what borrowing actually costs you over time.
The math behind the breakdown is standard amortization. You enter the balance, the annual rate and the payment you make. For any given month, interest equals the outstanding principal times the monthly interest rate (annual rate / 12), and whatever is left of the payment reduces the principal; the calculator repeats that month by month to count the months to payoff and the total interest. Daily interest is shown as the balance times the annual rate / 365.
Rates shift, particularly on variable-rate loans, so it is worth revisiting your numbers periodically. Borrowers on income-driven repayment plans see an especially different picture, since a low capped payment can tilt heavily toward interest and even trigger negative amortization, where the balance climbs instead of falling. Directing extra money straight at principal works in the opposite direction, cutting both your total interest and the length of the loan.
Example: A $30,000 Undergraduate Direct Loan at the 2026-27 Rate
- 1 Input: a $30,000 undergraduate Direct Unsubsidized Loan first disbursed between July 1, 2026 and June 30, 2027, which carries a fixed 6.52% rate, repaid at $341 a month, roughly what a 10-year term requires.
- 2 Interest: $30,000 × 6.52% / 12 = $163.00 in the first month, or $5.36 a day ($30,000 × 6.52% / 365).
- 3 Split: of the $341 payment, $163.00 (47.8%) goes to interest and $178.00 to principal.
- 4 Payoff: repeating that month by month, the calculator shows payoff in 120 months (10.0 years) with $10,911.45 of total interest. As the balance falls, each payment's interest share shrinks and more of it goes to principal.
Source: Federal Student Aid — Federal interest rates and fees · Last updated: September 2026
Frequently Asked Questions
How much student loan interest do I pay each month?
Does paying extra on student loans reduce interest?
Is student loan interest simple or compound?
You might also need
Student Loan IDR Comparison — IBR vs PAYE vs ICR Plans
Compare the Income-Driven Repayment plans side by side: IBR, PAYE and ICR (SAVE ended in March 2026). See monthly payments, total cost, and forgiveness. Free, instant results.
Student Loan Refinance Calculator
Compare current student loans vs refinanced terms. See monthly savings, total interest savings, and break-even point.
PSLF Calculator (Public Service Loan Forgiveness)
Track progress toward Public Service Loan Forgiveness. See payments remaining, forgiveness amount, and total cost.