Investment Calculator
Project investment growth with monthly contributions, annual raises, fund expense ratios and inflation — with a yearly split of what you invested vs. earned.
Investment Calculator: with the default inputs, ending value is $300,850.72.
The S&P 500 has averaged about 10% a year before inflation since 1926, roughly 7% after.
- Total invested
- $130,000Starting amount plus all contributions.
- Investment gains
- $170,851
- Fees paid to the fund
- $0Approximate dollars lost to the expense ratio, not counting the growth those dollars would have earned.
- Ending value in today's dollars
- —
Assumptions
- Returns compound monthly at a constant rate; contributions arrive at the end of each month.
- The expense ratio is subtracted from the annual return; fees shown are the approximate dollars deducted, not their lost growth.
- No taxes, trading costs or advisory fees beyond the expense ratio.
| Year | Contributed | Gain this year | Total invested | Balance |
|---|---|---|---|---|
| 1 | $6,000 | $919 | $16,000 | $16,919 |
| 2 | $6,000 | $1,419 | $22,000 | $24,339 |
| 3 | $6,000 | $1,956 | $28,000 | $32,294 |
| 4 | $6,000 | $2,531 | $34,000 | $40,825 |
| 5 | $6,000 | $3,148 | $40,000 | $49,973 |
| 6 | $6,000 | $3,809 | $46,000 | $59,782 |
| 7 | $6,000 | $4,518 | $52,000 | $70,299 |
| 8 | $6,000 | $5,278 | $58,000 | $81,578 |
| 9 | $6,000 | $6,094 | $64,000 | $93,671 |
| 10 | $6,000 | $6,968 | $70,000 | $106,639 |
How this is worked out
The formula
Each month: Balance = Balance × (1 + r) + Contribution r = (annual return − expense ratio) ÷ 12 Contribution rises by the step-up percentage at the start of each year Closed form with level contributions: FV = Start × (1 + r)^n + PMT × [ (1 + r)^n − 1 ] ÷ r, n = years × 12
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Starting amount
- A number.in dollars · 0 or more · defaults to 10000
- Monthly contribution
- A number.in dollars · 0 or more · defaults to 500
- Expected annual return
- The S&P 500 has averaged about 10% a year before inflation since 1926, roughly 7% after.a percentage · from -50 to 100 · defaults to 7
- Years invested
- A number.from 0 to 80 · whole numbers only · defaults to 20
- Annual contribution increase(under More options)
- Raise your monthly amount each year, e.g. 3% to track pay rises.a percentage · from 0 to 50 · defaults to 0
- Fund expense ratio(under More options)
- Broad index funds charge 0.03–0.20%; actively managed funds often 0.5–1%.a percentage · from 0 to 5 · defaults to 0
- Show ending value in today's dollars(under More options)
- Turn this on or off.defaults to off
- Inflation rate(under More options)
- A number.a percentage · from 0 to 50 · defaults to 3
What you get back
- Ending valuemain answer
- Total invested
- Starting amount plus all contributions.
- Investment gains
- Fees paid to the fund
- Approximate dollars lost to the expense ratio, not counting the growth those dollars would have earned.
- Ending value in today's dollars
What this assumes
- Returns compound monthly at a constant rate; contributions arrive at the end of each month.
- The expense ratio is subtracted from the annual return; fees shown are the approximate dollars deducted, not their lost growth.
- No taxes, trading costs or advisory fees beyond the expense ratio.
About this calculator
Whether $500 a month turns into $250,000 or $400,000 depends almost entirely on three things: the return you actually earn after fees, how many years you stay invested, and whether you raise the contribution as your income grows. This calculator lets you set all three and shows, year by year, how much of the final figure is your money and how much is growth.
How to use it
Enter what you're starting with, the monthly amount, an expected return and the horizon. Leave the return honest: a diversified stock portfolio has returned about 10% a year before inflation over the last century, bonds about 5%, and a 60/40 mix somewhere between. Open More options to add a yearly contribution increase (3% roughly matches wage growth), your fund's expense ratio, and an inflation adjustment so the ending value is in money you can picture. Solve for works backwards: "what monthly amount gets me to $1 million by 60?"
Reading the results
- Ending value is the nominal balance at the end.
- Total invested vs gains is the split worth staring at. Over 30 years at 7%, gains are roughly two-thirds of the pile — the money is doing more work than you are.
- Fees paid is the cash skimmed by the expense ratio. A 1% fund on a portfolio that reaches $500,000 quietly takes about $5,000 a year at the end; a 0.05% index fund takes $250.
- Today's dollars deflates the ending value by inflation. It's the number to compare against today's prices.
What the model leaves out
Returns arrive in lumps, not a smooth 7%. The order of good and bad years matters little while you're contributing, and a lot once you start withdrawing. Taxes aren't modelled — in an IRA or 401(k) there are none along the way; in a taxable account dividends and realised gains trim the return by perhaps half a percentage point a year. And the calculator can't know your behaviour: the biggest determinant of real-world results is whether you keep contributing through the years the chart goes down.
Frequently asked questions
▸What return should I assume?
For a diversified stock portfolio, 6–7% after inflation (9–10% nominal) matches the long-run US record; for bonds, 1–2% real. Using a lower figure than history and being pleasantly surprised beats the opposite.
▸How much difference does an expense ratio make?
A lot over decades. On $500 a month for 30 years at 8%, a 1% fee leaves you with about $150,000 less than a 0.05% index fund — roughly a fifth of the final balance.
▸Is it better to invest a lump sum or monthly?
Historically a lump sum invested immediately beats spreading it out about two-thirds of the time, because markets rise more often than they fall. Monthly investing is what most people can actually do, and it smooths the ride.
▸Does the calculator include taxes?
No. In a 401(k), IRA or ISA nothing is taxed while it grows. In a taxable brokerage account, dividends and any gains you realise are taxed each year, lowering the effective return somewhat.
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