Cernarus

Student Loan Interest Calculator

This calculator models student loan amortization under multiple payment-frequency methods: standard monthly payments, direct bi‑weekly (26 payments per year), and accelerated bi‑weekly that pays half the monthly payment every two weeks. Use it to compare estimated interest paid and time to payoff when you add recurring extra payments.

Results are estimates. They assume interest compounds at the stated APR with no fees, capitalization, loan-specific enrollment changes, deferments, or forgiveness programs. Always verify with your servicer for exact payoff amounts and to confirm how extra payments are applied.

Updated Nov 6, 2025

Make 26 equal payments per year (payment frequency = every two weeks). This method uses periodic interest for 26 periods per year and treats extra_payment as additional amount applied each bi‑weekly payment.

Inputs

Results

Updates as you type

Base payment (per bi‑weekly)

$150.13

Estimated payoff time (years)

—

Estimated interest paid

—

Estimated total paid

—

OutputValueUnit
Base payment (per bi‑weekly)$150.13currency
Estimated payoff time (years)——
Estimated interest paid—currency
Estimated total paid—currency
Primary result$150.13

Visualization

Methodology

We compute a periodic interest rate by dividing the annual interest rate (APR) by the number of scheduled payments per year for the chosen method (12 for monthly, 26 for bi‑weekly).

We calculate the fixed base payment that amortizes the principal over the scheduled number of periods using the standard annuity formula. When an extra payment amount is entered, we add it to the base payment for each scheduled period and estimate the reduced number of payments required to reach zero balance using logarithmic amortization inversion.

For the half‑monthly bi‑weekly method we first compute the monthly base payment, then apply half that monthly amount every two weeks. This commonly results in 26 half‑payments per year (equivalent to 13 full monthly payments) and typically reduces interest vs 12 monthly payments.

Worked examples

Example: $30,000 principal, 5.5% APR, 10-year term. Monthly base payment ≈ computed monthly base. Switching to bi‑weekly (26) with no extra payments reduces total interest because of the increased number of payments per year.

Example: Same loan with $25 extra applied each bi‑weekly payment accelerates payoff and reduces interest substantially; the tool reports an estimated new payoff time and cumulative interest saved.

Expert Q&A

Why do bi‑weekly payments sometimes pay the loan off faster?

Direct bi‑weekly schedules create 26 payments per year instead of 12, increasing the number of payments and the amount of principal applied each year. When using half‑monthly payment methods, paying half the monthly payment every two weeks results in the equivalent of 13 full monthly payments per year, shortening the term.

Does this calculator account for loan servicer rules or capitalization?

No. This model is a mathematical amortization estimator. Loan servicers may apply payments, fees, or capitalization differently. Confirm payoff amounts and rules with your servicer before making changes.

Are results exact?

Results are estimates produced by standard amortization formulas. Small differences can occur due to rounding, exact day counts, interest accrual conventions, or servicer processing rules. Use the estimate for planning and verify with statements or your servicer for precise payoff numbers.

How should I apply extra payments to get the fastest payoff?

Directing extra amounts toward principal each payment cycle is generally the most effective. Confirm with your servicer that extra payments are applied to principal rather than future payments, and obtain written confirmation if needed.

Sources & citations