Fidamen

Home Loan Extra Payments Calculator with Bi-Weekly Payments

This calculator provides estimates for mortgage payments, payoff timing, and interest savings when making bi-weekly or other periodic payments and when adding extra principal payments (recurring or one-time). It models level-payment (fully amortizing) loans and assumes interest compounds per scheduled period.

Results are intended for planning and comparison only. Actual lender behavior, escrow, fees, prepayment penalties, and rounding can change exact outcomes. Verify final figures with loan documents or your lender.

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

Governance

Record c41fa03e75fb • Reviewed by Fidamen Standards Committee

Calculates the regular payment, total paid and total interest for a level-payment amortizing loan using the entered payments per year.

Inputs

Results

Updates as you type

Scheduled payment (per period)

—

Number of payments (periods)

—

Total paid over life of loan

—

Total interest paid

—

OutputValueUnit
Scheduled payment (per period)—USD
Number of payments (periods)—periods
Total paid over life of loan—USD
Total interest paid—USD
Primary result—

Visualization

Methodology

The tool computes a periodic interest rate by dividing the entered annual percentage rate by the number of payments per year. The base scheduled payment is derived from the level-payment amortization formula: payment = P * r / (1 - (1+r)^-N).

For recurring extras, the calculator increases the per-period payment and solves for the new number of periods using the closed-form logarithmic solution for an amortizing loan. For a one-time extra payment, the outstanding balance at the chosen period is computed and the reduced balance is re-amortized to estimate remaining payments.

Inputs must express payments per year explicitly (commonly 12 for monthly, 26 for bi-weekly). Using 26 models 26 identical periodic payments per year and the corresponding periodic rate; some lenders treat bi-weekly differently—check your loan terms.

F.A.Q.

Does entering 26 payments/year always match my lender's bi-weekly program?

Not always. Entering 26 simulates 26 equal payments per year and the periodic interest rate that results. Some lenders accept accelerated bi-weekly plans differently or require enrollment. Check your loan documents for how payments are applied and whether extra payments reduce principal immediately.

Are results exact for legal or tax reporting?

No. This calculator provides estimates. For legal, tax, or closing figures rely on lender statements, official amortization schedules, or a licensed mortgage professional.

How accurate are the formulas?

Formulas implement standard amortizing loan mathematics (time value of money and closed-form solutions). They assume constant interest rate, no fees, and that extra payments are applied directly to principal at the stated period.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: c41fa03e75fb

What changed (latest)

v1.0.0 • 2025-11-23 • 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 23, 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 • 2025-11-23 • 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: a72890ad8625