About the Investment Calculator
This investment calculator projects how much your money could grow. Enter a starting balance, how much you will add each month, an expected annual return and the number of years, and it shows your future balance, how much of it came from your own contributions and how much from compound growth.
It suits anyone investing in index funds, ETFs, a brokerage account, an IRA or a 401(k) who wants to answer “how much will my investment be worth?”. You can change how often returns compound, choose whether contributions go in at the start or end of each month, and add an inflation rate to see the result in today’s dollars.
The projection assumes a constant average return. Real markets rise and fall, so treat the result as an estimate and test a few return rates — for example 5%, 7% and 9% — to see a realistic range.
With the default inputs, the future value is $659,017.60. Change any value above to recalculate instantly.
How to use the investment calculator
- 1Enter how much you are starting with.
- 2Enter how much you will add every month.
- 3Choose an expected annual return — lower it to allow for fees and bad years.
- 4Set the number of years and, optionally, the compounding frequency and contribution timing.
- 5Review the future value, the growth vs. contributions split and the inflation-adjusted figure.
Formula and method
The starting balance grows with compound interest at the annual rate r, compounded k times a year. Monthly contributions are treated as an annuity: each deposit grows at the effective monthly rate i implied by your compounding choice, and the standard future-value-of-annuity formula adds them up. If you contribute at the start of each month, the annuity part is multiplied by (1 + i).
Growth is the future value minus everything you put in. The inflation-adjusted value divides the future value by (1 + inflation)^t so you can judge its purchasing power in today’s dollars. Taxes and fund fees are not deducted — lower the return rate to account for them.
- P
- Initial investment
- PMT
- Monthly contribution
- r
- Expected annual return
- k
- Compounding periods per year
- t
- Years invested
Worked examples
$25,000 plus $500 a month at 8% for 25 years
You contribute $175,000 in total, but monthly compounding at 8% grows it to about $659,018 — nearly $484,000 of it is investment growth. With 2.5% inflation that is worth about $355,468 in today’s dollars.
$10,000 plus $200 a month at 7% for 30 years
A modest $82,000 of contributions becomes about $325,159 after 30 years at 7%. Almost three-quarters of the final balance is growth. At 3% inflation it is roughly $133,961 in today’s money.
$1,000 a month, contributions at the start of the month, 6% for 10 years
Investing $1,000 at the start of every month for ten years at 6% builds about $164,699 from $120,000 of deposits. Contributing at the start rather than the end of each month earns one extra month of growth on every deposit.
Frequently asked questions
What rate of return should I use?+
Broad US stock indexes have historically averaged about 10% a year before inflation over long periods, or roughly 7% after inflation. A balanced stock-and-bond portfolio has returned less. Using 6–7% gives a more conservative plan.
How much will $500 a month be worth in 20 years?+
At an 8% average annual return compounded monthly, $500 a month grows to about $294,500 in 20 years from $120,000 of contributions. Enter your own numbers above to test different rates.
Does this include taxes and fees?+
No. Fund expense ratios, advisory fees and taxes all reduce real returns. A simple fix is to subtract your total yearly fees from the expected return — for example use 7.5% instead of 8% for a 0.5% fee.
Why does compounding frequency matter so little?+
Monthly versus annual compounding changes the effective yearly rate only slightly — 8% compounded monthly is 8.30% a year. The return rate, time invested and contribution amount matter far more.
What does the inflation-adjusted value mean?+
It converts the future balance into today’s purchasing power. At 2.5% inflation, prices roughly double every 28 years, so a large future balance will buy much less than the same amount would today.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.