Fidamen

Home Loan APR Calculator with Bi-Weekly Payments

This calculator estimates your periodic payment, total interest paid, effective annual rate (EAR), and an approximate payoff time when making bi‑weekly or other frequent payments or adding an extra amount each period. It is intended for planning and comparison, not as a formal loan disclosure.

The tool converts a nominal APR into per‑period rates based on the selected payment frequency (for bi‑weekly use 26). It shows how extra periodic contributions affect total interest and the estimated time to pay off the loan.

Updated Nov 3, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 02fb42ce69a5 • Reviewed by Fidamen Standards Committee

Inputs

Results

Updates as you type

Payment per period (includes extra payment)

$660.73

Scheduled number of payments

780

Total paid over life of loan (estimated)

$515,369.52

Total interest paid (estimated)

$215,369.52

Effective annual rate (EAR)

407.79%

Estimated payoff time (years) with extra payments

30

OutputValueUnit
Payment per period (includes extra payment)$660.73USD
Scheduled number of payments780—
Total paid over life of loan (estimated)$515,369.52USD
Total interest paid (estimated)$215,369.52USD
Effective annual rate (EAR)407.79%%
Estimated payoff time (years) with extra payments30—
Primary result$660.73

Visualization

Methodology

The calculator treats the loan as a fixed-rate amortizing loan. It derives the periodic payment from the annuity formula: A = r*P / (1 - (1+r)^-n), where r is the periodic interest rate and n is the total number of payments. If r is zero, payments equal principal divided by the number of periods.

Effective annual rate (EAR) is computed from the periodic rate as (1 + r)^(m) - 1, where m is the payment frequency per year. Estimates assume payments apply immediately to principal and interest according to the standard amortization schedule.

Calculation integrity and numeric stability follow general best practices for financial computations. For implementation and testing, follow IEEE floating point recommendations for numerical accuracy and, where required, align with ISO currency handling and NIST guidance on computational reproducibility.

F.A.Q.

Is this an official APR disclosure from my lender?

No. This calculator provides estimates for planning and comparison only. Lenders must provide an official Truth-in-Lending disclosure (or equivalent) that states the legal APR. Use this tool to explore scenarios but rely on lender documents for legal terms.

Why do bi‑weekly payments often reduce total interest?

With bi‑weekly payments (26 per year) you make the equivalent of 13 monthly payments in a year rather than 12. By increasing the payment frequency and/or making extra periodic contributions, you reduce principal earlier, which lowers the total interest over the life of the loan.

How accurate are the payoff time and savings estimates?

Estimates assume on‑time payments, no fees, no escrow adjustments, and that extra payments go directly to principal. Results are sensitive to rounding, compounding conventions, and how a lender applies partial payments. Consider small rounding differences and consult your lender for exact payoff figures.

What should I consider before moving to bi‑weekly payments?

Confirm with your lender whether they support bi‑weekly schedules, how they apply payments to principal and interest, and whether fees apply. Some services collect funds and issue a single monthly payment; the timing of principal reduction affects savings.

Which standards were used to guide the calculator design?

Design and numeric recommendations reference recognized standards bodies for computational integrity and financial data handling. See citations for general guidance from NIST, ISO, and IEEE.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: 02fb42ce69a5

What changed (latest)

v1.0.0 • 2025-11-03 • 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 3, 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 • 2025-11-03 • 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: 47e491ae3842