Personal Loan Extra Payments Calculator
This calculator models how extra principal applied each payment period shortens the loan term and reduces total interest for either a monthly schedule (12 payments per year) or a bi‑weekly schedule (26 payments per year). Enter the loan amount, APR, term, and the extra principal you will add to each period's payment.
Results include the scheduled payment without extra principal, the adjusted payment with extra principal, the estimated number of payments until payoff, payoff time in years, total amount paid and total interest paid. Use the monthly method to represent standard monthly payments; use bi‑weekly to simulate half‑month payments that occur 26 times per year.
Standard amortization with 12 payment periods per year. Enter extra principal applied each monthly payment period.
Inputs
Results
Scheduled monthly payment (no extra)
$193.33
Monthly payment (with extra principal)
$193.33
Number of payments until payoff
—
Time to payoff (years)
—
Total interest paid
—
Total amount paid
—
| Output | Value | Unit |
|---|---|---|
| Scheduled monthly payment (no extra) | $193.33 | — |
| Monthly payment (with extra principal) | $193.33 | — |
| Number of payments until payoff | — | payments |
| Time to payoff (years) | — | years |
| Total interest paid | — | — |
| Total amount paid | — | — |
Visualization
Methodology
We use standard amortization formulas for fixed‑rate installment loans. The scheduled payment is calculated from the principal, periodic interest rate and scheduled number of periods using the annuity formula.
When an additional amount is applied to principal each period, the calculator computes the effective number of payment periods required to retire the loan by solving the amortization equation for the number of periods. All calculations assume interest compounds at the same periodic frequency as payments and that extra principal reduces outstanding principal immediately.
Precision and numerical functions follow common computing practices; results are rounded for display. For formal verification of software behavior and numerical stability, refer to national and international standards for software reliability and numeric computations.
Further resources
Expert Q&A
Does the calculator assume extra payments always reduce principal immediately?
Yes. The model applies extra principal to the outstanding balance on the same date the regular payment is applied, which reduces the next period's interest accrual.
How do I represent making a single extra payment each month versus each bi‑weekly pay period?
Enter the additional amount per payment period in the 'Extra principal' field for the schedule you are evaluating. For monthly comparisons, enter the extra amount you will add each month. For bi‑weekly comparisons, enter the extra amount you will add each bi‑weekly period.
Are assumptions about compounding and payment timing important?
Yes. This tool assumes interest compounds and is applied at the same periodic frequency as payments. Different lender rules (daily interest, interest capitalization timing, fees, or prepayment penalties) will change real outcomes; consult your loan documents.
How accurate are the results?
Results use closed‑form algebraic solutions to the amortization equations and standard mathematical functions. Small numerical differences may occur due to rounding and the display precision. For regulatory or tax reporting, use lender statements or official amortization schedules.
Sources & citations
- National Institute of Standards and Technology (NIST) — https://www.nist.gov
- International Organization for Standardization (ISO) — https://www.iso.org
- Institute of Electrical and Electronics Engineers (IEEE) — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — https://www.osha.gov