Cernarus

Student Loan Payment Calculator with Extra Payments

This calculator estimates how recurring extra payments or a one-time lump-sum payment change the time to pay off a student loan and the total interest paid. Enter your current balance, APR, remaining term, payment frequency, and any extra payments to see results for multiple scenarios.

Results are provided for two methods: adding a fixed amount to each scheduled payment, and applying a lump-sum reduction after a chosen number of payments then continuing with recurring extras. Use the scenario that matches your plan.

Updated Nov 27, 2025

Applies a fixed additional amount to each scheduled payment and computes reduced payoff time and interest.

Inputs

Results

Updates as you type

Scheduled payment (no extra)

$318.20

Payment with recurring extra

$318.20

Estimated time to payoff

10

Total interest paid

$8,183.59

Interest saved vs. no extra payments

$0.00

OutputValueUnit
Scheduled payment (no extra)$318.20—
Payment with recurring extra$318.20—
Estimated time to payoff10years
Total interest paid$8,183.59—
Interest saved vs. no extra payments$0.00—
Primary result$318.20

Visualization

Methodology

Calculations use standard amortization mathematics for fully amortizing installment loans. The scheduled (no-extra) payment is computed with the standard formula for an annuity.

When recurring extras are provided, the calculator treats the extra amount as an additional principal payment each period and recomputes the number of periods until the balance reaches zero using the closed-form logarithmic solution for an amortizing loan.

For a lump-sum application, the remaining balance is computed at the lump moment using the amortization balance formula, the lump-sum is subtracted, and the remaining payoff schedule is recomputed using the recurring payment (including any recurring extra).

Worked examples

Example 1: $30,000 balance, 5% APR, 10 years remaining, monthly payments. Adding $50 to each monthly payment shortens the payoff and reduces total interest; the calculator shows years remaining and interest saved.

Example 2: Same loan, apply $5,000 after 12 months, then add $50 extra each payment thereafter. The tool shows the new payoff time and total interest compared to no extra payments.

Key takeaways

Use the recurring-extra method to model adding the same amount to every scheduled payment. Use the lump-sum method to model a one-time principal reduction followed by recurring extras.

Results are illustrative; confirm with your loan servicer for exact payoff dates and amounts.

Further resources

External guidance

Expert Q&A

How accurate are these estimates?

Estimates use standard closed-form amortization formulas and assume interest is compounded at the scheduled interval and payments are applied as specified. Results are numeric estimates; actual amounts may differ slightly due to lender rounding, timing, daily interest accrual, capitalization, or payment application order. See accuracy notes below.

What if my loan has variable interest rates, fees, or deferment periods?

This calculator assumes a fixed APR and uninterrupted payments. Variable rates, fees, deferments, forbearance, interest capitalization, or income-driven repayment plan rules are not modeled. For those cases, use your servicer's statements or an official loan simulator and treat these results as illustrative.

Are extra payments always applied to principal?

This tool assumes recurring extra payments and lump sums reduce principal immediately. Actual allocation depends on your loan servicer's policies. Confirm with your servicer how extras are applied and whether they reduce next payments or principal.

Do you store or transmit my inputs?

This configuration documents behavior only. Implementations should follow security standards such as NIST SP 800-series for data protection and privacy when storing or transmitting user data.

Sources & citations