Compound growth is the closest thing to a financial superpower that ordinary people have access to. Money that grows earns returns on its returns — and over decades, this turns modest monthly contributions into serious wealth. This calculator shows you exactly what consistent investing looks like over your chosen timeframe.
Step 1. Enter your starting amount — the money you have available to invest today. This can be zero.
Step 2. Add your planned monthly contribution and the expected annual return rate.
Step 3. Choose your time horizon. The longer it is, the more dramatic the compounding effect becomes.
With the default inputs loaded in the form, the calculator produces a starting result you can use as a baseline. Change one field at a time to compare a new scenario.
The most powerful variable in compound growth isn't the return rate — it's time. A 25-year-old investing $300/month at 8% will have more money at 65 than a 35-year-old investing $600/month at the same return. Ten years of extra compounding time doubles the outcome even with half the monthly contribution. This is why starting early matters far more than the exact amount.
An 8% annual return is a reasonable long-term assumption for a diversified stock market index fund. Some years will be higher, some significantly lower — in 2022, the S&P 500 dropped over 18%. But the long-run historical average for the US stock market is close to 10% nominal, or 7% after inflation. The calculator works best when you're thinking in decade-long horizons.
The gap between what you contribute and what the calculator projects as your final balance is entirely the result of compounding. If you contribute $200/month for 30 years, you put in $72,000. At 8%, your balance could be over $270,000. That extra $198,000 came from your returns earning their own returns — not from you.
For long-term stock market investing, 7–8% after fees is a commonly used conservative assumption. For bonds, 3–4%. For a mixed portfolio, 5–6%. Always use rates net of fees — a 1% annual expense ratio has a larger long-term impact than most people expect.
This calculator uses monthly compounding, which is standard for most investment and savings accounts. It produces slightly better results than annual compounding over long periods.
If the investments are in a tax-advantaged account like a 401(k) or Roth IRA, taxes on growth are deferred or eliminated. For taxable accounts, reduce your expected return by roughly 0.5–1% to account for annual capital gains distributions.
Enter your monthly income and key expense categories to instantly see your surplus, deficit, and savings rate.
Add up your assets and liabilities to calculate your real net worth — the true measure of your financial position.
Calculate your emergency fund target based on monthly expenses and see exactly how much more you need to save.
See your monthly cash flow by comparing income against fixed expenses, variable expenses, and savings allocations.
Disclaimer: Results from this calculator are for informational and planning purposes only and do not constitute financial, legal, or professional advice. Always verify important calculations with a qualified professional.
