Fidamen

Home Loan Interest Calculator

This calculator compares standard monthly amortization to bi‑weekly payment schedules for a home loan. Enter the loan amount, annual interest rate (APR), term in years, and any optional additional amount you plan to add to each bi‑weekly payment.

Results show the estimated monthly and bi‑weekly payment amounts, total interest paid under each schedule (using 26 bi‑weekly periods per year), estimated interest savings, total paid under a bi‑weekly schedule, and an approximate payoff time when making bi‑weekly payments including extras.

Updated Nov 6, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record a6ee6d22581c • Reviewed by Fidamen Standards Committee

Inputs

Results

Updates as you type

Estimated monthly payment (no extra)

$1,347.13

Estimated bi‑weekly payment (base + extra)

$621.48

Total interest paid with monthly payments

$184,968.26

Total interest paid with bi‑weekly payments (assumes 26 periods/year)

$184,753.30

Estimated interest saved (monthly − bi‑weekly)

$214.96

Total amount paid with bi‑weekly schedule

$484,753.30

Approximate payoff time with bi‑weekly payments (years)

—

OutputValueUnit
Estimated monthly payment (no extra)$1,347.13USD
Estimated bi‑weekly payment (base + extra)$621.48USD
Total interest paid with monthly payments$184,968.26USD
Total interest paid with bi‑weekly payments (assumes 26 periods/year)$184,753.30USD
Estimated interest saved (monthly − bi‑weekly)$214.96USD
Total amount paid with bi‑weekly schedule$484,753.30USD
Approximate payoff time with bi‑weekly payments (years)—years
Primary result$1,347.13

Visualization

Methodology

Calculations use standard amortization formulas converting the annual nominal rate to the period rate (monthly = annual/12, bi‑weekly = annual/26) and the standard annuity formula for level payments. For zero interest rate the calculator uses linear repayment to avoid division by zero.

This tool provides deterministic mathematical estimates for comparison and planning. It does not account for lender-specific policies (for example, whether your lender applies bi‑weekly payments as credited halves of a monthly payment, posts payments immediately, or applies payments toward principal on receipt). Use the results for planning and discuss exact payoff timing with your lender.

F.A.Q.

Does a bi‑weekly schedule always save interest?

Generally yes when bi‑weekly payments result in an extra equivalent monthly payment each year or when additional per‑payment principal is applied. Savings depend on exact payment amount, timing, and how the lender posts payments.

Why do some calculators show different savings for the same inputs?

Differences come from modeling choices: whether bi‑weekly is treated as 26 equal payments per year, whether half‑monthly payments are used, how interest is compounded, and whether lender posting rules or prepayment penalties are modeled.

How accurate are these estimates?

Estimates use standard amortization mathematics but are approximate for real‑world payoff timing. They do not substitute for lender statements or escrow/tax/fee calculations. See accuracy caveats and standards references below.

Sources & citations

Further resources

External guidance

Versioning & Change Control

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

Record ID: a6ee6d22581c

What changed (latest)

v1.0.0 • 2025-11-06 • 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 6, 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 • 2025-11-06 • 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: 46196ce825f4