Fidamen

Home Loan Amortization Calculator with Bi-Weekly Payments

This amortization calculator compares common bi‑weekly approaches and shows estimated payments, total amount paid and estimated interest over the nominal schedule. It supports a direct bi‑weekly compounding method and the accelerated (half monthly) method so you can compare outcomes side‑by‑side.

Results are computed from standard annuity formulas; where exact payoff timing depends on iteration and remaining principal, the tool reports nominal schedule estimates and includes caveats about rounding and day‑count conventions.

Updated Nov 22, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 490e5a9cbad4 • Reviewed by Fidamen Standards Committee

Calculates a bi‑weekly payment using the bi‑weekly interest period (annual rate / 26) and the full set of bi‑weekly payments over the contractual term.

Inputs

Advanced inputs

Loan inputs

Payment options

Results

Updates as you type

Bi‑weekly payment

$621.48

Number of bi‑weekly payments (nominal)

780

Total paid (nominal)

$484,753.30

Total interest (nominal)

$184,753.30

Estimated years to payoff

30

OutputValueUnit
Bi‑weekly payment$621.48USD
Number of bi‑weekly payments (nominal)780payments
Total paid (nominal)$484,753.30USD
Total interest (nominal)$184,753.30USD
Estimated years to payoff30years
Primary result$621.48

Visualization

Methodology

Direct bi‑weekly method uses an interest period of 1/26 of the annual rate and computes payments for term_years * 26 periods. This directly models lenders that compound on bi‑weekly cycles.

Accelerated bi‑weekly method first computes the monthly annuity payment then uses half that amount every two weeks. Because there are 26 bi‑weekly payments per year this typically yields an effective extra monthly payment per year and accelerates payoff.

Both methods allow an extra fixed contribution per bi‑weekly payment. The calculator uses closed‑form annuity formulas for nominal schedules; it does not perform a full per‑payment amortization loop in the browser for exact payoff dates when extra payments shorten the loan — see accuracy notes below.

F.A.Q.

Does this give exact payoff date when I add extra payments?

No. Outputs use nominal payment counts (term_years * 26) and closed‑form sums for comparability. Adding extra payments reduces principal faster in reality; an exact payoff date requires a per‑payment iterative amortization schedule which depends on lender day‑count and payment application rules.

Which method saves more interest?

Generally the direct bi‑weekly compounding and accelerated (half monthly) approaches both reduce interest versus monthly payments because you make more frequent payments; exact savings depend on rate, term and extra payments. Use the two modes here to compare nominal totals.

How accurate are these numbers?

This tool uses standard annuity formulas and reports nominal schedule totals. Differences may arise from lender rounding, day‑count conventions, exact interest application dates, escrow, fees, and prepayment rules. Treat results as estimates; for loan payoff planning get an itemized amortization schedule from your lender.

What standards guide the calculator's reliability and data handling?

Computation and software quality practices align with general standards such as NIST guidance on numeric algorithms and verification, ISO software quality best practices, and IEEE recommendations for numerical accuracy. For data handling and workplace safety references, consult relevant OSHA and organizational policies.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: 490e5a9cbad4

What changed (latest)

v1.0.0 • 2025-11-22 • 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 22, 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 • 2025-11-22 • 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: 15f0fc9649b1