About Lamuko

Lamuko is an independent website that builds free, accurate personal-finance calculators, starting with mortgage payoff tools for US homeowners.

Our approach

We believe financial math should be transparent. Every calculator shows its formula, includes a worked example and produces a full amortization schedule so you can check each number. Our shared calculation library is covered by automated tests against well-known reference values, such as the $1,896.20 monthly payment on a $300,000, 30-year loan at 6.5%.

How we calculate

Every calculator runs on one shared, open amortization engine. The scheduled payment uses the standard fixed-rate formula M = P × r / (1 − (1 + r)⁻ⁿ), where r is the annual rate ÷ 12. Each month we charge interest on the remaining balance, round it to the cent as loan servicers do, apply principal and any extra payment, and shorten the final payment so it never overpays. Biweekly results are modeled the way most servicers credit them (one extra payment a year, applied monthly), with an optional true 26-period mode. Recasts re-amortize the post-lump-sum balance over the remaining term. Refinance break-even compares both loans month by month and counts payment savings, cash costs and the difference in balances.

How we check accuracy

• Reference values. Automated tests check results against standard published figures, for example $1,896.20 a month for $300,000 at 6.5% over 30 years, $954.83 for $200,000 at 4%, and $790.79 for $100,000 at 5% over 15 years.
• Invariants. Tests confirm that principal paid always adds up to the loan amount, that schedules end at exactly $0, and that a 30-year loan has exactly 360 payments.
• Edge cases. 0% rates, lump sums larger than the balance, and refinances with identical terms are tested.
• Real browser. Every page is opened in a real browser before release and its numbers are checked against the same reference values.
• Plain-language review. Articles are reviewed against public guidance from the Consumer Financial Protection Bureau, Freddie Mac and Fannie Mae, which we link as sources on each page.

Privacy by design

All calculations run locally in your browser. Nothing you type is sent to our servers.

Not financial advice

Lamuko provides educational tools only. We are not a lender, broker or financial adviser. Please consult a qualified professional and your loan servicer before making decisions.

Contact

Spotted an error or have a calculator request? Get in touch.