Free Investment Calculator

See how your money grows

Enter any amount, any monthly contribution, and any time horizon — and watch compound interest do its work.

Inputs
Initial Investment Amount you invest today
$
Monthly Contribution How much you add each month
$
Annual Return Rate 7% — Historical average
% per year
1% Conservative 4–6% Aggressive 10–12% 15%
Time Horizon 20 years
years
1 yr 10 20 30 50 yrs
Compound Frequency How often interest compounds
Investment Growth Over Time
Total Balance
Contributions
Year-by-Year Breakdown
Year Total Contributed Interest Earned Balance
How compound interest actually works

The most powerful force in personal finance — explained without jargon.

What is compound interest?
Simple interest pays you interest only on your original deposit. Compound interest pays you interest on your deposit and on all the interest you have already earned. Over time, the difference becomes enormous.
Why time is the most important variable
$10,000 invested for 10 years at 7% grows to $19,672. The same $10,000 invested for 30 years grows to $76,123. The extra 20 years adds almost $57,000 — without investing a single additional dollar. Starting earlier matters more than investing more later.
What return rate should you use?
The United States stock market has returned an average of approximately 10% per year before inflation, and roughly 7% after adjusting for inflation. For conservative estimates, use 6–7%. For aggressive scenarios, use 9–10%. Avoid anything above 12% — it is not realistic long-term.
Frequently asked questions
What is a realistic annual return to expect?
The historical average annual return of the United States stock market (specifically the S&P 500) is approximately 10% before inflation, or 7% after adjusting for inflation. For a diversified portfolio of index funds, 6–8% is a reasonable long-term expectation. More conservative portfolios with bonds typically return 4–6%. Never plan around returns above 12% for long-term projections.
How does monthly compounding differ from annual compounding?
With annual compounding, interest is calculated once per year on your balance. With monthly compounding, interest is calculated 12 times per year — meaning each month's interest earns interest the following month. On a $10,000 investment at 7% annual rate over 20 years, monthly compounding yields approximately $400 more than annual compounding. The difference grows significantly with larger amounts and longer time horizons.
Is this calculator accounting for taxes and inflation?
No — this calculator shows nominal growth without adjusting for taxes or inflation. In reality: (1) Investments in taxable accounts are subject to capital gains tax when sold; (2) Investments in a Roth IRA grow tax-free; (3) Inflation of approximately 2–3% per year erodes purchasing power. To get an inflation-adjusted estimate, subtract 2–3 percentage points from your expected return rate. For tax-advantaged accounts like a Roth IRA, the numbers shown are closer to your real take-home result.
What is the best way to invest money long-term?
For many beginners, a common long-term approach is: (1) Learn whether a Roth IRA fits your situation; (2) Consider low-cost total market index funds such as VTI or FSKAX; (3) Set up automatic monthly contributions; (4) Avoid emotional trading during market downturns. This approach still carries risk, but it keeps costs low and reduces decision fatigue.
How much should I invest each month?
A common starting guideline is 15% of your gross income toward retirement. However, the most important thing is consistency — even $100 per month invested starting at age 25 grows to approximately $263,000 by age 65 at a 7% annual return. Use the Monthly Contribution calculator above to find the exact amount you need to reach any specific goal.