A student loan calculator estimates a repayment balance, monthly payment, and interest from the loan amount, annual rate, repayment term, and a grace period you enter. It can also model an extra monthly payment.
This tool uses a generic fixed-rate amortization model. It does not determine eligibility for a federal repayment plan or reproduce a loan servicer's schedule. Check your loan documents and servicer for the actual balance, payment, and dates.
Inputs and calculation assumptions
- Loan amount: Enter a positive balance. The calculator accepts up to $1 billion.
- Annual interest rate: Enter a fixed rate from 0% to 20%. The model divides it by 12 for monthly interest.
- Repayment term: Enter a whole number of months from 1 to 300. This term determines the amortization schedule. Not sure of the term? Federal standard repayment is 120 months.
- Grace period: Enter 0 to 24 months. The model estimates simple interest during this period and adds it to the balance before repayment.
- Repayment plan: Choose Standard, Graduated, Extended, or Income-Driven (IDR). What this selector does and does not change is stated once under Important limitations below.
- Extra monthly payment: Optionally enter an additional amount applied to each modeled repayment month.
- Repayment start date: Optionally enter the date of the first payment. The calculator uses this date to display timeline and extra-payment savings estimates.
How the grace-period estimate works
The calculator estimates grace-period interest as:
Grace-period interest = original loan balance x (annual rate / 12) x grace-period months
It adds that amount to the original balance and amortizes the resulting balance over the repayment term. For example, $30,000 at 5% with a 6-month modeled grace period accrues $750 in grace-period interest, producing a repayment balance of $30,750.
For a 120-month repayment term, the estimated monthly payment is $326.16. The calculator reports $8,387.90 in interest over the repayment schedule and $39,137.90 total repaid. The $8,387.90 figure is repayment-period interest; it does not include the separate $750 grace-period interest. The model's estimated grace-period cost compared with starting repayment without the grace period is $954.41, because the capitalized amount also accrues interest during repayment. At the $326.16 modeled payment, that $954.41 is roughly the value of three monthly payments.
A recent graduate scenario, which is the case these inputs fit: $30,000 of unsubsidized loans at 5% enters a 6-month grace period and the 120-month standard term. The grace period models the months between leaving school and the first payment, during which interest on an unsubsidized loan typically accrues unpaid, and the 120-month term matches federal standard repayment. On those inputs the model estimates $750.00 of grace-period interest, a $30,750.00 repayment balance, a $326.16 monthly payment, $8,387.90 of repayment-period interest, and the $954.41 grace-period cost described above. Whether a given loan actually capitalizes at that point depends on its subsidy status and terms, which the model does not test.
Repayment and extra-payment estimates
The monthly payment is calculated using a standard reducing-balance formula. Each modeled payment covers interest for the month and applies the remainder to the balance. The final payment can be slightly different because the schedule rounds amounts to cents.
With the same $30,750 repayment balance and 5% rate, an additional $100 per month produces an estimated payment of $426.16 and $5,901.33 in repayment-period interest. When a repayment start date is entered, the calculator reports 33 fewer payment months and $2,486.57 less interest than the base schedule. Actual savings depend on when the servicer receives and applies extra payments.
How the repayment term changes the cost
With the $30,750 repayment balance and the 5% rate held constant, the term is the only variable:
| Term | Monthly payment | Repayment interest | Total repaid | Extra interest against the 120-month term |
|---|---|---|---|---|
| 120 months (10 years) | $326.16 | $8,387.90 | $39,137.90 | Baseline |
| 240 months (20 years) | $202.94 | $17,954.13 | $48,704.13 | +$9,566.23 |
| 300 months (25 years) | $179.77 | $23,175.93 | $53,925.93 | +$14,788.03 |
Doubling the term from 10 to 20 years cuts the payment by $123.22 and adds $9,566.23 of interest. Extending it from 20 to 25 years cuts another $23.17 a month and adds another $5,221.80, which means sixty more payments are being made to save less than $25 a month. The payment flattens out long before the interest does. The totals above exclude the $750 of grace-period interest already added to the balance, and they assume the loan is held to term rather than refinanced or forgiven.
Important limitations
The grace-period input is a modeling assumption, not a statement that a particular loan offers a grace period or that interest will capitalize under its contract. Some loans may receive an interest subsidy during certain periods, and capitalization events vary by loan type and applicable rules. This calculator treats all interest estimated during the entered grace period as added to the repayment balance.
The plan names do not make this a federal-plan estimator, and this is the one place that limitation is stated in full. The repayment-plan selector changes the displayed label and explanatory note only; it does not change the payment formula. The tool does not calculate payments from income or family size, assess eligibility, model forgiveness, distinguish subsidized from unsubsidized loans, or determine tax consequences. It also does not model daily accrual, variable rates, multiple loan groups, or a servicer's payment-allocation rules.
Federal repayment options and eligibility are governed by current program rules, not this generic amortization model. Review the Federal Student Aid repayment-plan information and confirm your individual payment with your servicer.
For a different loan-payment estimate, use the Loan Payment Calculator. To examine a payment-by-payment principal and interest schedule, try the Amortization Calculator. If you are comparing a new interest rate or term, use the Student Loan Refinance Calculator.
Enter the balances and rates as your servicer lists them. For the dollar payoff amount at a date rather than the full repayment plan, use the Loan Payoff Calculator.
Last verified: October 2026. Calculator figures are outputs for the inputs entered; they are not live quotes, current rates, or an offer.