Student Loan Amortization Calculator
This calculator compares standard monthly amortization, a biweekly annuity approach (26 equal payments per year), and the commonly used accelerated biweekly technique where you pay half of the monthly payment every two weeks. It reports scheduled payment amounts, estimated payoff time, total amount paid, and interest paid under each scenario.
Results are estimates intended for planning and comparison. Small implementation differences (billing cycle, how servicers apply extra payments, leap years, and interest day-count conventions) can change real-world outcomes. See methodology and caveats below.
Common accelerated strategy: pay half of the standard monthly payment every two weeks. This results in 26 half-payments (13 full-month equivalents) and typically shortens the term. Payoff time is estimated by solving the annuity equation for the number of biweekly periods.
Inputs
Results
Biweekly payment (half of monthly)
$106.07
Estimated biweekly payments to payoff
234.428
Estimated years to payoff
9.0165
Total paid
$24,864.73
Interest paid
$4,864.73
| Output | Value | Unit |
|---|---|---|
| Biweekly payment (half of monthly) | $106.07 | USD |
| Estimated biweekly payments to payoff | 234.428 | periods |
| Estimated years to payoff | 9.0165 | years |
| Total paid | $24,864.73 | USD |
| Interest paid | $4,864.73 | USD |
Visualization
Methodology
All formulas use nominal annual interest rate (APR) converted into periodic rates by dividing by the number of periods per year. Monthly computations use 12 periods; biweekly computations use 26 periods. The standard annuity formula is used to compute level payments that amortize the loan over the stated term.
The accelerated biweekly mode models the typical consumer strategy of paying half the monthly payment every two weeks. This creates 26 half-payments per year (equivalent to 13 full payments), which effectively applies one extra monthly payment per year. Payoff time for that strategy is estimated by solving the annuity equation for the number of periods given a fixed per-period payment.
Accuracy and safety checks: the tool assumes payments are applied immediately and that the servicer compounds interest at the same periodic frequency. If a servicer applies interest daily or applies extra payments first to future payments instead of principal, results may differ. This tool does not replace official payoff quotes from your loan servicer.
Worked examples
Example: $20,000 at 5.0% APR for 10 years. Standard monthly payment uses periods_per_year=12 and N=120. Accelerated biweekly using half-monthly payments uses payment = monthly_payment/2 and periods_per_year=26; solving for N shows a shorter payoff and lower total interest.
Example: If you enter an extra payment amount, the calculator treats it as an additional amount applied each scheduled payment period and re-estimates payoff time and total interest accordingly.
Key takeaways
Monthly amortization gives the baseline scheduled payment and total cost.
Biweekly annuity computes payments sized for 26 periods/year and the same term; amounts differ because period length differs.
Accelerated biweekly (half-monthly every two weeks) is modeled by fixing the biweekly payment to half the monthly payment and solving for the resulting payoff time; this typically reduces interest paid by creating effectively one extra monthly payment per year.
Further resources
Expert Q&A
Will this calculator match my loan servicer's payoff exactly?
No. This tool provides estimates. Servicer specifics such as daily interest calculation, how extra payments are applied, payment posting times, and contract terms can change the exact payoff date and total interest. Always request an official payoff quote from your loan servicer for an exact figure.
Which method should I use to save the most interest?
Generally, making more frequent payments or extra principal payments reduces total interest by lowering outstanding principal sooner. The accelerated biweekly approach commonly reduces interest compared with standard monthly payments, but true savings depend on your servicer's posting rules. Use the accelerated biweekly mode here for a quick estimate.
What if my servicer charges interest daily or compounds differently?
This calculator assumes periodic compounding consistent with the chosen frequency. If your loan compounds daily or uses a different day-count convention, the calculator's estimates may differ from actual amortization. Consult your servicer or a financial advisor for a servicer-specific schedule.
Are leap years or extra days accounted for?
No. This tool uses period counts (12, 26) and does not model calendar dates or leap years. For date-accurate amortization schedules use an amortization engine that accepts exact payment dates and your servicer's day-count rules.
Sources & citations
- National Institute of Standards and Technology (NIST) — Guidance on Numerical Accuracy — https://www.nist.gov
- International Organization for Standardization (ISO) — https://www.iso.org
- IEEE — Recommended Practices for Numerical Computation — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — risk and process documentation guidance — https://www.osha.gov