Fidamen

Mortgage Extra Payments Calculator

This calculator models standard monthly amortization and a bi‑weekly payment option with recurring extra payments. Use it to estimate new payoff timing, approximate interest savings, and how each added contribution shortens the loan.

Results are estimates based on a fixed interest rate and do not account for prepayment penalties, escrow changes, variable rates, or lender rounding and timing policies. Verify plan details with your lender before changing payment schedules.

Updated Nov 4, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 4a9c65340b01 • Reviewed by Fidamen Standards Committee

Estimate results when using a bi‑weekly payment frequency and adding recurring extra payments. Converts annual rate to per‑payment rate for 26 payments per year and accounts for extra contribution per bi‑weekly payment.

Inputs

Results

Updates as you type

Base bi‑weekly payment (no extra)

$621.48

Bi‑weekly payment with extra

$621.48

Estimated payoff time (years)

30

Months saved vs original term

0

Estimated interest saved

$0.00

Number of bi‑weekly payments until payoff

780

OutputValueUnit
Base bi‑weekly payment (no extra)$621.48USD
Bi‑weekly payment with extra$621.48USD
Estimated payoff time (years)30years
Months saved vs original term0months
Estimated interest saved$0.00USD
Number of bi‑weekly payments until payoff780payments
Primary result$621.48

Visualization

Methodology

Monthly amortization is computed using the standard fixed-rate annuity formula converting APR to a per-period rate and solving for payment that amortizes the principal over the term.

Bi‑weekly calculations convert APR to a per‑payment rate for 26 payments per year. Recurring extra contributions are translated into an equivalent additional amount per bi‑weekly payment when the user specifies monthly or yearly extra amounts.

To estimate payoff time with extra payments we solve the standard amortization equation for the number of payments required given the increased payment amount. All computations use continuous numeric math; results are rounded for display.

Key takeaways

This tool provides quick comparative estimates between standard monthly amortization and a bi‑weekly schedule with recurring extra payments. Use results for planning only and confirm with your lender for precise payoff figures.

Technical accuracy adheres to common numeric computation practices; users should consider rounding and lender posting policies when interpreting savings and payoff dates.

F.A.Q.

Is switching to bi‑weekly always better than monthly?

A bi‑weekly schedule can reduce interest and shorten payoff if implemented as 26 payments per year and not merely by splitting monthly payments. Savings depend on interest rate, extra amounts, and whether the lender applies payments immediately to principal. Check for prepayment rules.

Does this calculator include taxes, insurance, or escrow?

No. This tool models principal and interest only. Escrow, taxes, insurance, PMI, and fees are excluded and must be handled separately.

How accurate are these estimates?

Estimates follow standard amortization mathematics and typical per‑period conversions. They are subject to rounding, floating point limits, and do not capture lender-specific posting rules or prepayment penalties. For regulatory and technical accuracy guidance consult standards such as NIST and IEEE; consult your lender for contract‑level figures.

Can extra payments be applied as one‑time lumps in this tool?

This version focuses on recurring extras and equivalent per‑payment conversions. One‑time lump sums are not modelled explicitly here; consult your lender or use a dedicated payoff planner to model single large prepayments.

Sources & citations

Further resources

External guidance

Versioning & Change Control

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

Record ID: 4a9c65340b01

What changed (latest)

v1.0.0 • 2025-11-04 • 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 4, 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 • 2025-11-04 • 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: baa5942db2f7