Free finance calculators with transparent assumptions
FinTools is a set of free, browser-based calculators for compound interest, investing, retirement, 401(k) contributions, debt payoff, and APY. Every calculator shows its formula, assumptions, and limitations next to the result.
Calculators
Compound Interest Calculator Estimate how balances may grow from principal, contributions, rate, and time. Investment Calculator Project investment balances with contributions, return assumptions, inflation, and fee drag. Retirement Calculator Project whether savings may last through a planning age using transparent retirement assumptions. 401(k) Calculator Project 401(k) balances with salary contributions, employer match, 2026 limits, inflation, and fees. Debt Payoff Calculator Compare debt payoff timelines from balances, APRs, minimums, and extra payments. APY Calculator Convert APY and nominal annual rates with compounding frequency comparisons.
Educational only
FinTools pages are for general planning education, not financial, investment, tax, legal, or retirement advice.
Assumption-led
Calculators make inputs and assumptions visible instead of implying certainty about rates, returns, inflation, taxes, or personal outcomes.
Browser-first
Implemented calculators do not store inputs, call APIs, show live rates, or connect to financial accounts.