Methodology

Our principles

• Transparent formulas. Every calculator uses standard, publicly documented financial math.
• Conservative defaults. Default growth and inflation assumptions are intentionally moderate.
• Educational framing. Outputs are presented as estimates, not recommendations.
• Reviewable inputs. Every assumption a user can change is clearly labeled.

Compound interest & investment growth

Future value is calculated as FV = PV × (1 + r/n)^(n·t) + PMT × [((1 + r/n)^(n·t) − 1) / (r/n)], where r is the annual nominal rate, n is the compounding frequency, t is the number of years andPMT is the periodic contribution. Real (inflation-adjusted) values divide by (1 + i)^t using an assumed inflation ratei the user can edit.

Mortgage & amortization

Monthly payment uses the standard fixed-rate amortization formulaM = P × [c(1+c)^n] / [(1+c)^n − 1], where c is the monthly rate and n the total number of payments. We do not model PMI removal, escrow shortages, ARM resets, or jurisdiction-specific taxes unless explicitly noted on the calculator.

Retirement & FIRE projections

Retirement projections grow current balances and contributions at a user-specified nominal return, then withdraw at a user-specified withdrawal rate (default 4%, based on widely-cited safe-withdrawal research). They do not model sequence-of-returns risk, tax-bracket management, Roth-conversion ladders, Social Security claiming strategies, healthcare costs, or RMDs. Real-world outcomes vary materially.

Debt payoff

Avalanche and snowball strategies are simulated month-by-month using constant APRs and constant minimum payments. Real card APRs, fees, promotional periods and balance changes will affect actual payoff.

Inflation, taxes & fees

Unless a calculator is explicitly a tax calculator, results are pre-tax and exclude fund fees, advisor fees, trading costs and spreads. Federal, state, local and international tax rules vary by jurisdiction and year — verify with a qualified professional.

Known limitations

• Results assume constant rates and contributions unless the input UI says otherwise.
• We do not provide individualized projections or personalized advice.
• Past performance does not guarantee future results.

Review process

Calculator logic and assumptions are reviewed by the site's editor, Keiron Brown (see Editorial Standards) and updated when rules, rates or widely-accepted defaults change.