About Mortgage Number Lab

Each tool answers a different question:

• Mortgage Calculator— Estimate monthly principal, interest, taxes, insurance, PMI, and HOA in one payment figure.
• Scenario Comparison— Line up to three loan setups and compare payment, interest, and payoff timing.
• Payment Calculator— Monthly principal and interest only — loan amount, rate, and term.
• PMI Calculator— Estimate monthly PMI and loan-to-value from home price and down payment.
• Extra Payment— Model extra principal each month and see time and interest saved.
• Recast vs Refi vs Extra— Compare do-nothing, lump sum, recast, and refinance on the same loan.
• Affordability— Ballpark home price from income, debts, down payment, and DTI planning ratios.
• Refinance— Compare current vs new payment, cash break-even, and lifetime interest.
• Amortization— Full schedule of every payment’s principal, interest, and remaining balance.

A calculator is only useful if you can tell what it is doing. We aim for:

• Documented formulas on the Methodology page, including known limits.
• Assumptions listed near the results, not buried in fine print.
• Results framed as estimates for learning — not guarantees.
• Plain labels and short helper text when mortgage jargon shows up.

See the Methodology page for formulas, rounding notes, and limitations.

Math follows standard amortizing-loan formulas and is checked with automated unit tests against known reference values.

Outputs are still estimates. Your lender's rate, fees, credit profile, loan program, and local taxes can move the real number. Each calculator page calls out what it does not model.

If a result looks wrong, contact us with the inputs. Verified errors get fixed. The Editorial Policy covers corrections.

Mortgage Number Lab is not a lender, broker, bank, advisor, or real estate firm. We do not originate loans or take applications.

We do not have a stake in any particular lender. Ads do not change the formulas.

The site may show display ads through networks such as Google AdSense. Ads sit apart from the calculators and guides. Advertisers do not set formulas or editorial wording.

Data practices for ads are described in the Privacy Policy.

Content and results on Mortgage Number Lab are for education only. Nothing here is financial, legal, tax, or investment advice, and nothing is a loan offer or approval.

For decisions about your own loan, talk with a licensed mortgage professional or other qualified advisor. Full details are in the Financial Disclaimer.

Questions and error reports go through the Contact page.