Investing math you can check.
14 free calculators: 13 for long-term investors plus one trade-planning tool. Every page shows the exact formula and assumptions, works instantly in your browser, and is backed by automated tests, including a cent-for-cent match with the SEC's investor.gov compound interest calculator.
Calculators
Growing your money
Compound Interest Calculator
Monthly contributions, inflation adjustment, a withdrawal phase, any compounding frequency. Verified against the SEC's investor.gov calculator.
Open calculator →Dividend (DRIP) Calculator
Annual dividend income, yield on cost, and how reinvested dividends, dividend growth and price growth compound into shares and income.
Open calculator →Rule of 72 Calculator
How long it takes money to double at a given rate, and how close the rule of 72 is to the exact answer.
Open calculator →Goals & retirement
Savings Calculator
How much to save each month to reach a goal by a date, with interest (APY) and optional inflation.
Open calculator →Millionaire (Time to Goal) Calculator
How long until you reach $1 million or any amount, with your savings, contributions and return.
Open calculator →FIRE (Retire Early) Calculator
Your FIRE number using the 4% rule (an assumption you can change), years to financial independence and Coast FIRE.
Open calculator →401(k) Calculator
Your 401(k) at retirement with an employer match, raises and catch-up contributions, capped at the IRS limit (cited), plus any match you're missing.
Open calculator →Roth IRA Calculator
Roth IRA growth over time by age, with the current IRS contribution limit shown and cited.
Open calculator →Stocks, fees & taxes
CAGR (Annualized Return) Calculator
Compound annual growth rate from a start value, end value and years or exact dates.
Open calculator →Stock Average / Average Down Calculator
Average cost across multiple buys, break-even price, and how many shares you need to reach a target average.
Open calculator →Expense Ratio Calculator
What a 0.05% vs 1% expense ratio or advisory fee really costs over 10, 20 or 30 years (fee drag).
Open calculator →Tax-Loss Offset Calculator
US capital-loss netting: offset gains, deduct up to $3,000 from income, carry the rest forward. Estimate only.
Open calculator →Capital Gains Tax Calculator
Federal tax on a stock sale: short- or long-term, the 0%/15%/20% rates stacked on your income the IRS way, optional 3.8% NIIT. IRS figures cited. Estimate only.
Open calculator →Trade planning
Looking for trading software to go with the math? TraderToolStack compares charting platforms and trading journals, and lists what each tool's free plan includes.
Why trust these numbers?
One tested math engine
All calculations live in a single JavaScript module checked by an automated test suite of hand-computed values, closed-form formulas and edge cases.
Checked against outside sources
Compound interest matches the SEC's investor.gov calculator to the cent in all 13 scenarios we ran. Fee results agree with the rounded examples in the SEC's fee bulletin and with the closed-form formula. The remaining 12 of the 14 calculators are recomputed by separate Python programs using decimal arithmetic, and the tests require both to agree.
Assumptions in plain sight
Each calculator explains its formula, conventions and limits, with worked examples you can load and verify yourself.
Disclaimer: InvestorMath calculators give educational estimates, not financial, investment or tax advice. Results depend entirely on the assumptions you enter; real returns vary and are not guaranteed, and past performance does not predict future results. Check important decisions with a qualified professional.