Investment Calculator

Enter an initial investment, monthly contribution, expected annual return, and time period to calculate your final portfolio value, total return, and ROI.

Currency

Initial investment

Monthly contribution (optional)

$/ mo

Expected annual return

% / year

Time period

years

Final value

$58,785.61

Total invested

$34,000.00

Total return

$24,785.61

ROI

72.9%

Invested vs. Returns

Total invested (57.8%)Investment returns (42.2%)

How to use the Investment Calculator

Enter your initial investment
Type the amount you're investing upfront. This could be a lump sum into a savings account, ISA, index fund, or any other investment. Select your preferred currency using the buttons at the top.
Add a monthly contribution (optional)
If you plan to invest a fixed amount each month in addition to your lump sum, enter it here. Regular monthly contributions can dramatically accelerate long-term growth due to compounding.
Set the expected annual return
Enter your expected annual return rate as a percentage. Historically, global stock market index funds have returned around 7–10% annually before inflation. Conservative investments like bonds or savings accounts return much less.
Choose the time period
Enter the number of years you plan to invest. The year-by-year breakdown table shows how your investment grows over time.

About this Investment Calculator

Return on investment (ROI) is the most fundamental measure of investment performance — it tells you what percentage of your invested capital you've gained (or lost) over a period. Our investment calculator goes beyond a simple ROI percentage by modelling monthly compounding growth and regular contributions, giving a realistic picture of how a real investment portfolio might grow over time.

The calculation assumes monthly compounding with a fixed annual return rate. This is a reasonable approximation for diversified index funds or a savings account, but real returns vary year to year. The annual return you enter is the geometric mean — the equivalent fixed rate that would produce the same result as a fluctuating real-world return.

One of the most powerful concepts in investing is time. Due to compounding, an investment earning 8% annually doesn't just grow linearly — it grows exponentially. £10,000 invested at 8% for 10 years becomes approximately £21,600. Over 30 years, the same investment grows to roughly £100,600 — a 10-fold increase on the original capital. This is why starting early, even with a small amount, matters far more than the size of contributions later in life.

Monthly contributions amplify this effect further. Adding £200 per month to the same £10,000 at 8% over 10 years produces a final value of around £58,000 — more than double the lump-sum-only result. This illustrates why regular saving combined with investing, rather than timing the market, is the cornerstone of long-term wealth building.

Frequently Asked Questions

Return on Investment (ROI) is the percentage gain on your invested capital. ROI = (Total Return ÷ Total Invested) × 100. For example, if you invest £20,000 and end up with £35,000, your total return is £15,000 and ROI is 75%.

Historically, global stock market index funds have returned approximately 7–10% annually before inflation. Bonds and savings accounts typically return 2–5%. A conservative long-term planning estimate of 6–7% is commonly used by financial planners. Always remember that past performance doesn't guarantee future returns.

Monthly compounding means your returns are calculated and added to your balance every month, so next month's return is earned on a slightly larger balance. This produces modestly better results than annual compounding for the same stated annual rate — particularly over longer time periods.

Both matter, but consistent monthly contributions are often more impactful over time. They benefit from dollar-cost averaging (reducing the risk of investing a lump sum at a market peak) and allow you to invest funds as they become available. Starting with a lump sum and adding monthly contributions is typically the best combination.

No — this calculator shows nominal (pre-inflation, pre-tax) returns. To estimate real (inflation-adjusted) returns, reduce your expected annual return by the expected inflation rate (e.g. use 4% instead of 7% if inflation is 3%). Tax treatment depends on your jurisdiction and account type (ISA, pension, 401k, etc.).