Student Loan Extra Payment Impact Calculator
See how adding extra to your monthly student loan payment shortens your payoff time and reduces total interest paid.
Where the two payoff times come from
The balance B at monthly rate r (annual rate / 12) is solved for the number of level payments that reach zero - once at your payment, once with the extra:
months(P) = -ln(1 - B x r / P) / ln(1 + r)
interest = P x months(P) - BThe default payment is not arbitrary: $277.55 is exactly what clears $25,000 at
6% in ten years, from the same formula rearranged as
P = B x r / (1 - (1 + r)^-120). Left alone it costs $8,306 in
interest. Add $50 a month and payoff falls to 96 months, interest to $6,566 - two
years and $1,740 saved for $50.
Making sure the extra lands where you think
The model assumes every extra dollar hits principal the month you pay it. Servicers do not all behave that way: an overpayment is often treated as next month's bill paid early, which advances the due date and saves nothing. Ask in writing for extra amounts to go to principal, and if the account holds several loans, name the one to apply them to.
Frequently asked questions
How much does $50 a month extra save on a $25,000 student loan?
At 6% with a $277.55 payment, it cuts payoff from 120 months to 96 and saves $1,740 of interest. Doubling the extra to $100 gets you to 81 months and $2,868 saved.
Which loan should the extra payment go to?
The one with the highest rate, which is not always the largest balance. This calculator takes a single balance and rate, so run loans separately when their rates differ.
Does paying extra lower my monthly payment?
No - it shortens the schedule instead. The required payment stays put unless the loan is re-amortised, so the saving shows up as months removed from the end.