Investment Calculator
See the future value of your investment with regular contributions, total growth, your ROI, and the inflation-adjusted real value — with an instant verdict on whether you reach your goal, not just a number.
Calculator
Your investment
What this investment calculator does
An investment calculator projects how much your money could be worth in the future once you add a steady annual return and regular contributions. You enter a starting amount, how much you add each month, the years you stay invested, and an expected return. The tool then compounds everything month by month and shows four things competitors usually skip: the future value, the total growth (how much is pure interest versus your own deposits), your return on investment as a percentage, and the inflation-adjusted real value — what that future balance actually buys in today's money.
The result updates instantly as you type, so you can drag a single input and watch the outcome move. If you enter a goal, you also get a plain-English verdict telling you whether you are on track, close, or short — not just a raw number you then have to interpret yourself.
How to use it
- Starting amount — the lump sum you invest today (use 0 if you are starting from scratch).
- Monthly contribution — the amount you add every month, for example a recurring transfer into an index fund or 401(k).
- Years invested — your time horizon. Longer horizons benefit dramatically from compounding.
- Expected annual return — a realistic long-run average. The US stock market has historically returned roughly 7–10% before inflation; a balanced portfolio sits lower.
- Inflation rate — used to show the real (purchasing-power) value. 2–3% is a common long-run assumption.
- Goal amount — optional. Enter a target and the verdict tells you whether you make it.
The formula behind the numbers
The calculator combines two standard compound-growth formulas: the future value of your starting lump sum and the future value of a stream of monthly contributions (an annuity).
Future value of the lump sum: FVₕ = P × (1 + r)n
Future value of contributions: FVℂ = M × [ ((1 + r)n − 1) ÷ r ]
Total = FVₕ + FVℂ, where P = starting amount, M = monthly contribution, r = annual return ÷ 12, and n = months (years × 12).
To convert to today's money, the calculator divides the future value by (1 + inflation)years. That is why a balance that looks huge in 30 years often buys far less in real terms — a detail most "how much will my investment grow" tools ignore.
Worked examples
| Scenario | You contribute | Future value | Real value |
|---|---|---|---|
| $10,000 start + $500/mo, 8%, 30 yrs | $190,000 | $854,537 | $352,058 |
| $0 start + $300/mo, 7%, 25 yrs | $90,000 | $243,022 | $116,068 |
| $25,000 lump only, 7%, 20 yrs | $25,000 | $100,968 | $55,904 |
The first row shows the headline lesson: of the $854,537 final balance, only $190,000 is money you put in — the other $664,537 is compounding doing the work. But adjusted for 3% inflation, that pot is worth about $352,000 in today's spending power, which is the number you should actually plan around.
How return rate and time change the outcome
Two levers dominate every projection: your return rate and your time horizon. The table below shows the future value of $500 invested monthly (no starting lump) at different rates and lengths.
| Return | 10 years | 20 years | 30 years |
|---|---|---|---|
| 4% | ~$73,600 | ~$183,300 | ~$347,000 |
| 6% | ~$81,900 | ~$231,000 | ~$502,000 |
| 8% | ~$91,500 | ~$294,500 | ~$745,000 |
| 10% | ~$102,400 | ~$380,000 | ~$1,131,000 |
Notice how the gap between rates explodes over time. At 10 years, 4% versus 10% is a difference of about $29,000. At 30 years it is more than $780,000 on the exact same monthly deposit — which is why starting early and staying invested usually matters more than chasing the perfect entry point.
Common uses
- Retirement planning — project a 401(k), IRA, or pension pot and test whether your savings rate gets you there.
- Index-fund investing — model a monthly transfer into an S&P 500 or total-market fund over decades.
- Saving for a goal — a house deposit, a child's education, or a sabbatical fund with a fixed target.
- Comparing strategies — see whether a bigger monthly contribution or a higher-return portfolio gets you to the goal faster.
- Reality-checking returns — the inflation-adjusted figure stops you over-estimating how far a future balance will stretch.
Tips for realistic projections
- Use a conservative return. 7% is a reasonable long-run stock estimate before inflation; assuming 12% sets you up for disappointment.
- Always look at the real value. A million dollars in 30 years may only buy what ~$410,000 buys today at 3% inflation.
- Increase contributions over time. Even raising your monthly amount with your salary each year dramatically lifts the end result.
- Don't forget fees and taxes. A 1% fund fee quietly lowers your effective return — subtract it from the rate you enter.
- Time beats timing. The table above shows decades in the market outweigh small differences in when you start.
Frequently asked questions
What is a realistic rate of return to use?
For a long-term, diversified stock portfolio, 7–8% before inflation is a common planning assumption based on historical US market averages. A balanced stock-and-bond mix sits lower, around 5–6%. Avoid plugging in last year's hot return — use a long-run average and, if you want a margin of safety, round down.
Why does the calculator show a smaller "real value"?
Inflation erodes purchasing power, so a dollar in 30 years buys less than a dollar today. The real value divides your future balance by (1 + inflation) raised to the number of years, telling you what that future pot is worth in today's money. It is the most honest number for goal planning.
Does it assume monthly or annual compounding?
Monthly. The tool converts your annual return to a monthly rate and compounds every month, matching how most index funds, savings, and retirement accounts actually grow. Contributions are added each month and start compounding immediately.
What is the difference between this and a compound interest calculator?
They share the same engine, but this investment calculator focuses on growth over a long horizon with regular contributions, and adds ROI, an inflation-adjusted real value, and a goal verdict. If you only want to grow a single deposit, the compound interest calculator is the simpler tool.
Should I include taxes and fees?
This calculator shows gross growth. To approximate after-fee results, subtract your fund's expense ratio (often 0.03–1%) from the return you enter. Taxes depend on the account — tax-advantaged accounts like a Roth IRA or 401(k) grow tax-free or tax-deferred, while a taxable brokerage account is taxed on gains and dividends.
How much do I need to invest to reach $1 million?
It depends on your return and timeline. At an 8% return, about $500–$700 a month over 30 years gets most people there starting from a small base. Enter $1,000,000 as your goal, adjust the monthly contribution, and the verdict will tell you instantly when you cross the line.