S&P 500 Investment Calculator
Project the growth of a lump sum plus monthly contributions at a long-run index return you choose.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Explore a hypothetical investment scenario using the annual return you enter. The model compounds that nominal annual rate monthly and assumes contributions are made at the end of each month. It does not predict S&P 500 returns or include inflation, taxes, fees, dividends or market volatility.
Worked example
calculated with the default values below
Initial investment 10,000 $ · Monthly contribution 200 $ · Assumed annual return (scenario) 10 % · Investment period 20 years Projected value 225,154.50 $ · Total invested 58,000.00 $ · Investment growth 167,154.50 $
Method and assumptions
Formula basis and scope
End-of-month deposits use FV = D × ((1 + i)^n - 1) / i, with i = annual percent / 1200 and n = 12 × years; zero rate uses D × n. Existing savings also grow by (1 + i)^n.
Constant nominal rate and equal monthly deposits; excludes taxes, fees and inflation. It is a projection, not a guaranteed return. The entered return is hypothetical, not live S&P 500 data. Fractional month counts are mathematical projections, not an actual payment schedule.
Data sources
Disclaimer
These calculators give estimates for general information only. They are not financial, tax or investment advice and do not take your personal circumstances into account. Before borrowing, investing or filing, confirm the numbers with a qualified adviser in your jurisdiction.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
FV = P₀(1+r)^n + M × ((1+r)^n − 1) ÷ r; r = R÷100÷12, n = 12Y
- P₀
- Initial amount
- M
- Monthly contribution
- R
- Annual return (%)
- Y
- Years
The initial balance compounds monthly at annualReturn/12; recurring deposits are modeled at each month-end. This is a hypothetical scenario, not an S&P 500 return forecast; no inflation, tax, fees, dividends or volatility are modeled. The zero-rate case uses simple addition rather than division by zero.
Frequently asked questions
Does this predict future S&P 500 returns?
No. It applies your assumed rate to a hypothetical monthly-compounding scenario. Past performance does not predict future results, and actual outcomes can vary; fees and expenses also reduce returns. See the [SEC Investor Bulletin on performance claims](https://www.investor.gov/introduction-investing/general-resources/news-alerts/alerts-bulletins/investor-bulletins-47).