Fidamen

Home Loan Extra Payments Calculator

This calculator models how recurring extra payments or a single one‑time extra payment change the time to pay off a mortgage and the total interest paid. It supports monthly, bi‑weekly, and weekly payment schedules and compares results against a no‑extra baseline.

The tool provides estimates only and assumes a fixed interest rate and that extra payments are applied fully to principal on the same schedule as the regular payment. It does not account for prepayment penalties, escrow changes, variable rates, or lender processing rules.

Updated Nov 9, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 45a97aba9ea2 • Reviewed by Fidamen Standards Committee

Estimate payoff time and interest when you make a recurring extra principal payment each scheduled payment (works for monthly, bi‑weekly, weekly frequencies).

Inputs

Advanced inputs

Recurring extra settings

One-time extra settings

Results

Updates as you type

Scheduled regular payment

-$0.52

Total payment per scheduled period (incl. extra)

$49.48

Estimated payoff time (years)

—

Total interest paid (with extra)

—

Estimated interest saved

—

Estimated months saved

—

OutputValueUnit
Scheduled regular payment-$0.52USD
Total payment per scheduled period (incl. extra)$49.48USD
Estimated payoff time (years)—years
Total interest paid (with extra)—USD
Estimated interest saved—USD
Estimated months saved—months
Primary result-$0.52

Visualization

Methodology

All scheduled payment calculations use standard amortization formulas for fixed‑rate loans with periodic interest r = APR / payments_per_year and scheduled payment computed by the annuity formula.

When recurring extras are present, the calculator treats the extra as an additional principal payment each scheduled period and solves for the number of periods required to reduce balance to zero. For a one‑time extra, it computes the remaining balance immediately before the extra, reduces principal by the extra amount, and then solves for remaining periods.

Results are numeric estimates and are produced using common mathematical functions (exponentials and logarithms). Natural logarithms are used when solving for number of periods. Calculations follow recognized numerical practices for stability but are not a substitute for lender amortization schedules.

Worked examples

Example: $300,000 loan, 3.5% APR, 30 years, bi‑weekly (26) schedule, $50 extra every payment → shows reduced payoff time and interest saved versus baseline.

Example: $200,000 loan, 4.0% APR, 15 years, monthly schedule, $5,000 one‑time extra at payment 12 → computes new payoff date and interest savings.

F.A.Q.

Are these results exact for my loan?

These are mathematical estimates based on the inputs and standard amortization formulas. Actual results can differ because lenders may apply extra payments according to loan terms, have minimums, or charge prepayment fees. Always confirm with your lender for legally binding payoff figures.

Does bi‑weekly mean two half‑monthly payments?

Bi‑weekly (26 payments per year) is not the same as twice monthly (24 payments per year). This calculator treats bi‑weekly as 26 equal scheduled payments per year.

Will this account for adjustable rates or escrow changes?

No. The calculator assumes a fixed interest rate for the remaining life of the loan. For adjustable-rate mortgages or loans with escrow changes, results are only illustrative.

What about rounding and numerical limits?

Calculations use standard floating‑point arithmetic. Very small interest rates or extremely high frequencies can produce rounding effects. For critical financial decisions, consult a licensed professional and request an official payoff statement from your lender.

Sources & citations

Further resources

External guidance

Versioning & Change Control

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

Record ID: 45a97aba9ea2

What changed (latest)

v1.0.0 • 2025-11-09 • 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 9, 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 • 2025-11-09 • 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: 8ebdf7ca6e34