Fidamen

Mortgage Fixed Rate Calculator

This fixed-rate mortgage calculator estimates periodic principal-and-interest payments for a standard fully-amortizing fixed-rate loan and adds common escrowed items (annual property tax, homeowners insurance, HOA). Results are illustrative and intended for planning. This calculator does not generate a loan commitment or substitute for a lender’s disclosure.

Accuracy and reliability: values depend on input precision and assumptions (for example, taxes and insurance assumed evenly distributed across periods). For system and calculation quality we align practices with recognized standards for mathematical accuracy and software reliability such as NIST guidance on reproducible computation, ISO software quality management principles, and IEEE recommendations for algorithmic validation. Use conservative rounding and confirm final figures with your lender.

Updated Nov 2, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record ea53b6918143 • Reviewed by Fidamen Standards Committee

Inputs

Results

Updates as you type

Loan amount (purchase price − down payment)

$240,000.00

Periodic principal & interest payment

-$2.36

Total periodic payment (PI + taxes/insurance/HOA)

$397.64

Total paid over loan term (all periodic payments + escrow totals)

$143,150.00

Total interest paid (over life of loan, principal only)

-$240,850.00

OutputValueUnit
Loan amount (purchase price − down payment)$240,000.00USD
Periodic principal & interest payment-$2.36USD
Total periodic payment (PI + taxes/insurance/HOA)$397.64USD
Total paid over loan term (all periodic payments + escrow totals)$143,150.00USD
Total interest paid (over life of loan, principal only)-$240,850.00USD
Primary result$240,000.00

Visualization

Methodology

Compute the loan principal as purchase price minus down payment.

Compute the periodic interest rate by dividing the annual APR by 100 and then by the chosen number of payments per year.

Use the standard fixed-payment loan amortization formula to compute periodic principal-and-interest payment: payment = r * PV / (1 - (1+r)^-n) where r is periodic rate, PV is loan principal, n is total number of payments.

Add prorated escrow items per period: property tax and insurance divided by the number of payments per year, plus monthly HOA converted to the chosen periodic unit by adding the monthly amount directly for monthly frequency (for other frequencies HOA is included as monthly*12/periods-per-year).

F.A.Q.

Does this calculator include closing costs and lender fees?

No. Closing costs, lender fees, mortgage insurance, and points are not included in the main payment calculations. Enter those amounts separately when comparing loan offers or add them to the purchase price if you wish to see their effect on the loan amount.

How does changing payments per year affect results?

Payments per year changes the periodic rate and number of periods. For the same APR and term, increasing payment frequency (for example, biweekly) will slightly reduce interest paid over the loan life if the lender applies payments immediately to principal. This calculator uses strict amortization math and assumes all payments are applied per schedule.

What if interest rate is zero?

The standard amortization formula divides by (1 - (1+r)^-n). If r equals zero, the principal & interest payment should be calculated as loan_amount / n. This tool assumes a positive APR; for a true zero-rate loan, divide principal evenly by the number of payments.

Is this a legally binding disclosure?

No. This calculator provides estimates only and is not a Loan Estimate, Closing Disclosure, or commitment. Always consult a licensed lender and review official loan documents.

Sources & citations

Further resources

External guidance

Versioning & Change Control

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

Record ID: ea53b6918143

What changed (latest)

v1.0.0 • 2025-11-02 • 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 2, 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 • 2025-11-02 • 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: ef4c6fa6888e