US Student Loan Repayment Calculator

The US student loan repayment calculator compares four repayment-style monthly payments using the formulas implemented in the form: standard fixed, extended fixed, SAVE-style income-driven, and PAYE or IBR-style income-driven. It is designed for borrowers who want to understand why an official-looking monthly bill can differ so much depending on the plan structure. The result is an educational estimate, not an official Federal Student Aid quote.

Federal student loan rules are not static. Plan availability, SAVE litigation, income-driven repayment regulations, interest treatment, poverty-guideline updates, family-size certification, and forgiveness timelines can change. This calculator therefore explains the mechanics it uses rather than pretending to predict every official servicer result. Use the estimate as a comparison aid, then confirm current options through StudentAid.gov and your loan servicer.

Inputs and what they mean

Enter the federal student loan balance, the average annual interest rate, your adjusted gross income, and family size. Then choose the repayment plan you want to highlight. The selected plan becomes the main result, but the calculator still displays all four payments so you can compare them.

The fixed plans depend on balance, rate, and term. The standard plan uses 120 months. The extended plan uses 300 months. The income-driven plans depend on income above an allowance tied to family size. The form’s poverty guideline function starts with $15,650 for a family size of one and adds $5,500 for each additional family member. That guideline is a calculator assumption and may differ from future official figures.

For related planning, use the student loan forgiveness calculator to project balances left after a qualifying-payment timeline, the student loan payment calculator for a fixed payoff term, and the budget calculator to fit the payment into monthly cash flow.

Fixed repayment formula

For standard and extended plans, the calculator uses the standard amortization formula:

$\text{monthly payment} = \frac{P \times r}{1 - (1 + r)^{-n}}$

Here, P is the loan balance, r is the monthly interest rate, and n is the number of months. If the interest rate is zero, the calculator divides the balance evenly across the term.

The standard plan uses n = 120. The extended plan uses n = 300. The longer term usually lowers the monthly bill but raises the time in repayment and can increase total interest.

Income-driven formulas in this calculator

The calculator first estimates the poverty guideline:

$\text{guideline} = \$15{,}650 + \max(0, \lceil \text{family size} \rceil - 1) \times \$5{,}500$

Then it estimates discretionary income and divides by twelve:

$\text{IDR monthly payment} = \frac{\max(0, \text{AGI} - \text{guideline} \times \text{multiplier}) \times \text{assessment rate}}{12}$

For the SAVE-style estimate, the multiplier is 2.25 and the assessment rate is 5%. For the PAYE or IBR-style estimate, the multiplier is 1.5 and the assessment rate is 10%. The calculator does not model loan mix, spousal income rules, caps tied to standard payment, interest subsidies, or official recertification details.

Worked example matching the default inputs

Assume a borrower enters a $35,000 federal loan balance, a 5.5% average interest rate, $55,000 of AGI, family size 1, and selects the SAVE-style income-driven plan. The poverty guideline used by the compute function is $15,650.

The standard ten-year payment is about $379.84 per month. The extended twenty-five-year payment is about $214.93 per month. Those results come from amortizing $35,000 at 5.5% over 120 and 300 months.

For the SAVE-style estimate, the allowance is 2.25 × $15,650 = $35,212.50. Discretionary income is $55,000 - $35,212.50 = $19,787.50. Five percent of that is $989.38 per year, and dividing by twelve gives about $82.45 per month.

For the PAYE or IBR-style estimate, the allowance is 1.5 × $15,650 = $23,475. Discretionary income is $31,525. Ten percent is $3,152.50 per year, or about $262.71 per month. With the SAVE-style plan selected, the main result is therefore $82.45 per month, while the comparison items show the other plan estimates.

How to interpret the comparison

The lowest monthly payment is not automatically the best choice. It may be the right short-term cash-flow decision, especially if the borrower is pursuing Public Service Loan Forgiveness or another valid forgiveness route. But if a borrower will repay in full, a lower monthly payment can leave more balance outstanding for longer. Interest subsidies, unpaid-interest rules, tax treatment, and forgiveness eligibility are critical details outside this simplified comparison.

The income-driven estimates also depend heavily on AGI and family size. A raise, marriage, divorce, child, change in tax filing status, or updated poverty guideline can change the official payment. Revisit the calculation whenever income or household size changes, and keep documents needed for servicer certification.

Common mistakes

• Using gross wages instead of adjusted gross income.
• Assuming the simplified SAVE-style formula is an official bill.
• Ignoring total interest because the monthly payment is lower.
• Forgetting that family size is rounded up in the poverty-guideline function.
• Comparing fixed and income-driven payments without considering forgiveness.
• Assuming rules will not change during a long repayment period.

Sources

• Federal Student Aid, Repayment plans — official overview of federal repayment options.
• Federal Student Aid, Income-Driven Repayment Plans — current federal guidance for IDR mechanics and applications.
• Federal Student Aid, Interest rates and fees — official student-loan interest-rate context.