On the standard 10-year plan, federal and most private student loans amortize like any fixed-rate loan. Any amount you pay above the required payment goes straight to principal, which shrinks future interest and pulls your payoff date forward.
How this calculator works
The required payment is calculated from your balance, rate and term using the standard loan payment formula.
The calculator then simulates the loan month by month twice — once with the required payment and once with your extra amount — and compares total interest and payoff time.
The formula
M = P × r / (1 − (1 + r)^−n)- M
- required monthly payment
- P
- loan balance
- r
- monthly rate
- n
- number of months
Worked example
A $35,000 balance at 6% over 10 years requires about $389 a month and costs roughly $11,600 in interest.
Adding $150 a month pays it off in about 6.6 years and saves around $4,200 in interest.
Tips
- Tell your servicer to apply extra payments to principal on the highest-rate loan, not to future payments.
- If you may qualify for Public Service Loan Forgiveness, paying extra can reduce the amount forgiven — check before prepaying.
- Refinancing federal loans into a private loan gives up federal protections such as income-driven repayment.
Frequently asked questions
Is there a penalty for paying student loans early?
No. Federal law prohibits prepayment penalties on federal and private student loans.
Should I pay off student loans or invest?
Compare your loan rate with your expected after-tax investment return. Many people pay extra on loans above about 6%–7% and invest when rates are low, after capturing any employer 401(k) match.
Does this work for multiple loans?
Enter the total balance and a weighted average rate for an estimate, or use the debt snowball vs avalanche calculator to model each loan separately.