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 our editorial team (see Editorial Standards) and updated when rules, rates or widely-accepted defaults change.