Methodology | PlainFigure

PlainFigure is not trying to replace a licensed financial professional. It is trying to make the first layer of financial math easier to inspect before a user talks to a lender, advisor, card issuer, or loan provider.

Deterministic math

For the same inputs, calculators return the same outputs. When randomness is needed, such as Monte Carlo retirement modeling, the scenario uses a visible seed so results are reproducible.

Private by default

Calculator inputs run in the browser. PlainFigure does not need account linking, loan documents, or personal identifiers to calculate estimates.

Independent results

Affiliate links may appear after results, but partner availability does not change formulas, outputs, or plain-English explanations.

Core calculation standards

Mortgage payment: principal and interest use the standard amortization formula. PITI pages add user-entered taxes, insurance, HOA, and PMI assumptions.

Mortgage comparison: loan offers are compared by monthly payment, total cost, points, fees, PMI, APR estimate, and break-even tradeoffs.

Affordability: home price is back-solved from front-end and back-end debt-to-income limits, then adjusted for down payment, rate, term, taxes, insurance, and HOA.

Debt payoff: payoff timelines use amortized interest accrual, monthly payments, transfer fees, promotional APR periods, and consolidation loan terms entered by the user.

Retirement Monte Carlo: annual returns are drawn from a normal distribution using the user's expected return and volatility assumptions. Success means the simulated portfolio does not hit zero before the final planned age.

Important limitations

Results are estimates, not approvals, quotes, recommendations, or guarantees.
Mortgage results do not include lender overlays, credit-score pricing adjustments, exact local taxes, lock periods, property eligibility, underwriting conditions, or final closing disclosures.
Debt and credit results do not guarantee issuer approval, credit limits, promotional APR availability, transfer limits, or post-promo interest treatment.
Retirement results do not model tax brackets, Social Security, pensions, required minimum distributions, healthcare shocks, account location, advisor fees, or behavioral spending changes.
Affiliate links and partner pages can help users compare products, but users should verify all rates, terms, fees, and eligibility with the provider.

How partner links are handled

PlainFigure can earn money when users click partner links and apply for financial products. That monetization belongs in clearly labeled call-to-action areas after a relevant result. It should not determine what the calculator says, which formula is used, or whether a scenario is described as good or risky.

PlainFigure needs active partner approvals before claiming specific affiliate relationships beyond generic public links. Until then, all public launch copy should stay conservative and disclose uncertainty plainly.

Source and review policy

Calculator explanations should cite durable public sources where useful: federal agency publications, lender disclosures, CFPB/HUD/IRS guidance, and well-known financial market conventions. Pages should show a last-updated date and be reviewed after major law, tax, mortgage, credit-card, or market convention changes.

PlainFigure calculator methodology is owned by the PlainFigure editorial team. PlainFigure does not currently claim review by a licensed financial adviser, mortgage professional, tax professional, attorney, or credit counselor.

Review means checking formulas, input labels, assumptions, result language, disclosures, and partner-link separation against the calculator's stated educational purpose. It does not mean underwriting, investment advice, tax advice, legal advice, or a guarantee that a provider will offer the terms modeled.

Formula example

Standard fixed-rate mortgage principal-and-interest payment:

payment = principal * monthlyRate / (1 - (1 + monthlyRate) ^ -termMonths)