What is Investment Return Calculator?

See how your money grows over time with compound interest. Enter your starting amount, monthly contributions, expected return rate, and investment period to get a year-by-year breakdown of your portfolio.

The math runs a compounding loop at your chosen frequency, so contributions made early in a year earn interest for the remaining months. Results split into principal versus growth and a yearly table shows the curve flatten or steepen depending on rate and time horizon. Two extras turn the projection into a planning tool: a Compare With Rate field that runs a second simulation in parallel for an optimistic vs. conservative read, and an inflation toggle that converts every year back to today's purchasing power so the final balance reflects real spending power, not headline dollars.

How to use

1. Enter your initial investment amount and any monthly contributions.
2. Set the expected annual return rate (e.g., 7% for stock market average) and investment period in years.
3. View the projected final value, total contributions, and total earnings in the results chart and table.

When to use

• Comparing a stock index fund versus a savings account over 10 or 30 years.
• Pricing the cost of skipping a $500 monthly contribution for one year.
• Checking how much earlier you can retire if returns average 8% instead of 6%.

Result

An investor enters $10,000 starting balance, $500 monthly contributions, 7% annual return, and 20 years. The calculator shows a projected balance of $300,850.72, with $130,000 from contributions and $170,850.72 earned from compound growth.

FAQ

Does the calculator account for inflation?

Yes, when you enable the inflation toggle. Set an expected annual inflation rate and the results card and year-by-year table will show a Real Balance column in today's dollars next to the nominal balance. With the toggle off, all figures stay in nominal future dollars without any adjustment.

What return rate should I use for stocks?

The S&P 500 has averaged around 10% annually over the past century, or roughly 7% after inflation. Many planners use 6-7% as a conservative assumption for a diversified stock portfolio held for the long term.

Are contributions added at the start or end of each month?

End of month. Each month the balance compounds once at the monthly rate (annual rate divided by 12), then the new contribution is added. This is the convention most retirement calculators use.

Why is my actual portfolio worth less than the projection?

The calculator assumes a constant return every year. Real markets move in chunks, so a 7% average over 20 years can include several down years that drag the running balance below the smooth projection at any given moment.

Can I model taxes or fund fees?

Not directly. Approximate it by lowering the return rate. For taxable accounts, drop 1-2 percentage points. For high-fee funds with a 1% expense ratio, subtract another full point. The CSV export lets you do detailed analysis in a spreadsheet.

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