Student Loan Payoff Calculator: Months & Interest 2026

How student loan payoff is worked out

A student loan payoff is worked out month by month: the monthly rate is the APR divided by 12, the month’s interest is the balance times that rate, the payment covers the interest first and then the balance, and the balance is simulated until it reaches zero. The last payment is just the balance plus that month’s interest, so it is smaller than the usual payment. The total interest is the sum of the monthly interest, and the total paid is the balance plus the total interest.

At the defaults — $30,000 balance, 6.8% APR, $350 a month — the first month’s interest is $30,000 × 6.8% ÷ 12 = $170.00, so $180.00 of the $350 payment touches the balance. The balance falls month by month, and after 118 months (9 yr 10 mo) it reaches zero, having cost $11,188.54 of interest and $41,188.54 in all. The last payment is $238.54. The standard 10-year plan is $345.24 a month with $11,428.92 of interest, so paying $350 a month saves $240.38 of interest and 2 months against it.

The worked example, line by line

Setup: $30,000 balance, 6.8% APR, $350 a month.

Line 1 — the monthly rate. 6.8% ÷ 12 = 0.5667% a month.

Line 2 — the first month’s interest. $30,000 × 6.8% ÷ 12 = $170.00 of interest in month 1.

Line 3 — the balance after month 1. $30,000 + $170.00 − $350.00 = $29,820.00. Only $180.00 of the payment touched the balance.

Line 4 — the long run. Each month the interest shrinks with the balance, so more of the $350 payment reaches the balance. Month after month, the loan takes 118 months (9 yr 10 mo) to reach zero.

Line 5 — the totals. The interest over all 118 months is $11,188.54, the total paid is $30,000 + $11,188.54 = $41,188.54, and the last payment is $238.54.

Reverse: a $591.21 a month payment clears the loan in 60 months; $345.25 in 120 months; $266.31 in 180 months; and $229.01 in 240 months. At $350 a month, the biggest balance gone in 120 months is $30,413.54, and in 60 months it is $17,760.21. Any balance above $61,764.71 never pays off at $350 a month and 6.8% APR.

Every branch, checked

$25,000 balance: the first month’s interest is $25,000 × 6.8% ÷ 12 = $141.67, so $208.33 of the $350 payment touches the balance. It takes 92 months (7 yr 8 mo), with $7,134.00 of interest and $32,134.00 paid in all. A $5,000 smaller balance takes 26 fewer months, because more of every payment reaches the balance.

$40,000 balance: the first month’s interest is $40,000 × 6.8% ÷ 12 = $226.67, so only $123.33 of the $350 payment touches the balance. It takes 185 months (15 yr 5 mo), with $24,605.81 of interest and $64,605.81 paid in all. A $10,000 bigger balance takes 67 more months, and costs more than twice the interest.

$20,000 balance: the first month’s interest is $20,000 × 6.8% ÷ 12 = $113.33, so $236.67 of the $350 payment touches the balance. It takes 70 months (5 yr 10 mo), with $4,235.92 of interest and $24,235.92 paid in all. A smaller balance pays off fast, because most of every payment reaches the balance.

APR 4.5%: the first month’s interest is $30,000 × 4.5% ÷ 12 = $112.50, so $237.50 of the $350 payment touches the balance. It takes 104 months (8 yr 8 mo), with $6,259.42 of interest and $36,259.42 paid in all. A lower APR saves $4,929.12 of interest, and 14 months.

APR 9%: the first month’s interest is $30,000 × 9% ÷ 12 = $225.00, so only $125.00 of the $350 payment touches the balance. It takes 138 months (11 yr 6 mo), with $18,229.08 of interest and $48,229.08 paid in all. A higher APR costs $7,040.54 more interest, and 20 more months.

APR 3%: the first month’s interest is $30,000 × 3% ÷ 12 = $75.00, so $275.00 of the $350 payment touches the balance. It takes 97 months (8 yr 1 mo), with $3,804.98 of interest and $33,804.98 paid in all. At 3% the loan costs barely more than a tenth of the balance in interest.

Payment $500 a month: the first month’s interest is still $170.00, so $330.00 of the $500 payment touches the balance. It takes 74 months (6 yr 2 mo), with $6,767.26 of interest and $36,767.26 paid in all. Paying $150 more a month saves 44 months and $4,421.28 of interest against the default.

Payment $250 a month: the first month’s interest is still $170.00, so only $80.00 of the $250 payment touches the balance. It takes 202 months (16 yr 10 mo), with $20,411.62 of interest and $50,411.62 paid in all. Paying $100 less a month costs 84 more months and $9,223.08 more interest.

Payment $450 a month ($100 extra): the first month’s interest is still $170.00, so $280.00 of the $450 payment touches the balance. It takes 84 months (7 yr), with $7,784.24 of interest and $37,784.24 paid in all. A hundred dollars extra a month saves 34 months and $3,404.30 of interest against the default.

Payment $300 a month: the first month’s interest is still $170.00, so $130.00 of the $300 payment touches the balance. It takes 148 months (12 yr 4 mo), with $14,397.28 of interest and $44,397.28 paid in all. Fifty dollars less a month costs 30 more months and $3,208.74 more interest.

Payment $200 a month: the first month’s interest is still $170.00, so only $30.00 of the $200 payment touches the balance. It takes 336 months (28 years), with $37,146.82 of interest and $67,146.82 paid in all. At $200 a month the loan costs more in interest than the balance itself, because the payment barely beats the interest.

Reverse — the payments for a payoff date: a $591.21 a month payment clears the $30,000 loan in 60 months; $345.25 a month clears it in 120 months (the standard 10-year plan); $266.31 a month clears it in 180 months; and $229.01 a month clears it in 240 months. At $350 a month, the biggest balance gone in 120 months is $30,413.54, and in 60 months it is $17,760.21.

Never-payoff threshold: at $350 a month and 6.8% APR, any balance above $61,764.71 never pays off, because the first month’s interest alone is more than $350. At $61,764.71 the first month’s interest is exactly $350.00, so nothing touches the balance; above it, the balance grows every month.

What the defaults assume

The model assumes a fixed APR, no new charges, no fees, and the same payment every month, so the balance only moves by the interest and the payment. It assumes the payment is applied to the interest first and then the balance, and it simulates month by month with unrounded running values, rounding only for display. It leaves out loan fees, capitalized interest, grace periods, deferment, forbearance and income-driven repayment plans, which change the payoff in real life. Rounding convention: money is rounded to cents, months are whole numbers, and all figures are computed from unrounded values, rounded only for display.

Output · formula · meaning

Who uses this

• The graduate with a $30,000 loan: they learn $350 a month takes 118 months and costs $11,188.54 of interest — so they know the loan is a 10-year plan, and they check the $450 a month case at 84 months before paying the minimum again.
• The borrower with a small balance: they learn a $20,000 balance takes 70 months and costs $4,235.92 of interest — so they know a smaller balance pays off fast, and they check the $25,000 case at 92 months before borrowing more.
• The borrower on a tight budget: they learn $200 a month takes 336 months and costs $37,146.82 of interest — so they know a small payment costs more in interest than the balance itself, and they check the $61,764.71 never-payoff threshold before cutting the payment.
• The borrower picking a payoff date: they learn $591.21 a month clears the loan in 5 years, and $266.31 a month takes 15 years — so they know the payment for the date they want, and they check the $30,413.54 maximum balance for 10 years at $350 a month before setting the amount.

Accuracy & limitations

The math is exact for the numbers you enter: the monthly interest is the balance times the APR divided by 12, the payment covers the interest first and then the balance, and the balance is simulated month by month with unrounded running values until it reaches zero. What the model cannot do is read your servicer’s statement for you: check the APR and the balance on the statement, because a 9% APR and a 3% APR give very different answers. It assumes a fixed APR, no fees, no capitalization, and the same payment every month, and it leaves out grace periods, deferment, forbearance and income-driven repayment. For paying the loan off faster, see how to pay off student loans faster; for the monthly payment itself, see student loan calculator.