Calculate how your money grows with compound interest and regular contributions.
How to Use This Investment Growth Calculator
Enter your starting investment amount, how much you plan to add each month, the expected annual return rate, and the number of years you'll invest. Choose your compounding frequency and optionally add an inflation rate to see your portfolio's real purchasing power. Hit Calculate Growth and instantly see your projected future value alongside a full year-by-year breakdown.
Why This Matters
The difference between starting to invest at 25 versus 35 can be staggering. Consider this: a $10,000 initial investment with $200/month at a 7% annual return compounds to roughly $528,000 over 30 years — but only $228,000 over 20 years. That's a $300,000 gap from just one extra decade.
This tool helps everyday investors, students, and financial planners visualize how time, rate, and regular contributions interact. Whether you're deciding between paying down debt or investing, planning for retirement, or exploring the impact of a pay raise on your savings, seeing the numbers side-by-side makes the abstract concrete. Even small changes matter — increasing your monthly contribution by $50 or snagging an extra 0.5% return can add tens of thousands of dollars over a long horizon.
Inflation adjustment is included because $500,000 in 30 years won't have the same buying power as today. With 2.5% average inflation, that future half-million is worth closer to $240,000 in today's dollars — still impressive, but worth knowing.
How It's Calculated
The calculator uses the Future Value of a Series formula, which combines a lump-sum compound interest formula with the future value of regular contributions:
FV = P × (1 + r/n)^(n×t) + PMT × [((1 + r/n)^(n×t) − 1) / (r/n)]
Where: P = principal (initial investment), r = annual interest rate (as a decimal), n = compounding periods per year, t = time in years, PMT = monthly contribution (annualized to match compounding period).
For inflation adjustment, the real value is: Real FV = FV / (1 + inflation_rate)^t
Interest earned each year is calculated incrementally so the year-by-year table accurately reflects compounding within each period.
Tips & Common Mistakes
- Don't underestimate compounding frequency. Daily compounding earns slightly more than monthly or annual — over 30 years, the difference adds up to hundreds or thousands of dollars on a large portfolio.
- Use realistic return rates. The S&P 500 has averaged ~10% nominal / ~7% real over long periods, but past performance doesn't guarantee future results. Use 6–8% for conservative projections.
- Always account for inflation. A 7% return with 2.5% inflation is really a ~4.4% real return. Don't plan retirement spending based on nominal future values alone.
- Contributions matter as much as rate. Consistent monthly contributions often outweigh chasing an extra percentage point of return — and carry no additional risk.
- This is a projection, not a guarantee. Markets fluctuate. Use this tool for planning and comparison, not as a financial promise. Consider consulting a financial advisor for personalized advice.
Frequently Asked Questions
What compounding frequency should I choose?
Most savings accounts and index funds compound monthly or daily, so "Monthly" is usually the most realistic choice. Bonds and some CDs compound semi-annually or annually. Choosing the correct frequency for your actual investment gives the most accurate projection — though the difference between daily and monthly compounding is often less than 0.1% on typical portfolios.
What annual return rate should I use?
It depends on your investment type. Broad stock market index funds (like S&P 500 ETFs) have historically returned around 10% nominally and 7% after inflation over long periods. Bonds average 3–5%, and savings accounts currently yield 4–5%. For a mixed portfolio, 6–7% is a common conservative estimate. Always stress-test with a lower rate (e.g., 5%) to see worst-case scenarios.
Why is my inflation-adjusted value so much lower?
Inflation compounds just like returns do — in reverse. At 2.5% annual inflation, prices roughly double every 28 years. So a future balance of $1,000,000 in 30 years has the purchasing power of about $477,000 in today's dollars. This is why most financial planners recommend targeting a real (inflation-adjusted) return rather than a nominal one.
Does this account for taxes on investment gains?
No — this calculator shows pre-tax growth. In taxable accounts, you'd owe capital gains tax when you sell, which reduces your net return. In tax-advantaged accounts like a 401(k) or Roth IRA, growth is tax-deferred or tax-free. For after-tax projections, reduce your effective return rate by your estimated tax drag (e.g., if you pay 15% on gains annually, reduce your rate by ~15%).