Fidamen

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.

Updated Nov 13, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record f6a978d01639 • Reviewed by Fidamen Standards Committee

Standard amortization with 12 payment periods per year. Enter extra principal applied each monthly payment period.

Inputs

Results

Updates as you type

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

—

OutputValueUnit
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——
Primary result$193.33

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.

F.A.Q.

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

Further resources

External guidance

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: f6a978d01639

What changed (latest)

v1.0.0 • 2025-11-13 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 13, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-13 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 20caedf21607