Investing math you can check.
Free calculators for long-term investors. 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 Reinvestment (DRIP) Calculator
See how reinvested dividends, dividend growth and share 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 Goal 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 →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 →Investment Fee (Fee Drag) Calculator
What a 0.05% vs 1% expense ratio or advisory fee really costs over 10, 20 or 30 years.
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 →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 7 scenarios. Fee results match the SEC's fee bulletin. Other calculators are recomputed by an independent Python program and checked against closed-form formulas.
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.