Index Calculator
Stock Index Calculator works out Ending balance and Investment growth from Amount invested today, Expected annual return and Compounding periods a year. The default figures on this page give ending balance of 37,696.71; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
4 steps
- Net return = 7% gross - 0.14% fund cost = 6.86% a year, compounded 1 times a year.
- Growth factor per period = 1 + 6.86/(100 * 1) = 1.0686.
- Lump sum alone: 10000 * (1 + r/n)^(n*t) over 20 years.
- Ending balance = 37696.71; of that, 27696.71 is investment growth on 10000 paid in.
Year-by-year balancetable
| year | contributions | withdrawals | interest | balance |
|---|---|---|---|---|
| 1 | 0 | 0 | 686 | 10,686 |
| 2 | 0 | 0 | 733.06 | 11,419.06 |
| 3 | 0 | 0 | 783.35 | 12,202.41 |
| 4 | 0 | 0 | 837.09 | 13,039.49 |
| 5 | 0 | 0 | 894.51 | 13,934 |
| 6 | 0 | 0 | 955.87 | 14,889.87 |
| 7 | 0 | 0 | 1,021.45 | 15,911.32 |
| 8 | 0 | 0 | 1,091.52 | 17,002.84 |
| 9 | 0 | 0 | 1,166.39 | 18,169.23 |
| 10 | 0 | 0 | 1,246.41 | 19,415.64 |
| 11 | 0 | 0 | 1,331.91 | 20,747.55 |
| 12 | 0 | 0 | 1,423.28 | 22,170.83 |
| 13 | 0 | 0 | 1,520.92 | 23,691.75 |
| 14 | 0 | 0 | 1,625.25 | 25,317.01 |
| 15 | 0 | 0 | 1,736.75 | 27,053.75 |
| 16 | 0 | 0 | 1,855.89 | 28,909.64 |
| 17 | 0 | 0 | 1,983.2 | 30,892.84 |
| 18 | 0 | 0 | 2,119.25 | 33,012.09 |
| 19 | 0 | 0 | 2,264.63 | 35,276.72 |
| 20 | 0 | 0 | 2,419.98 | 37,696.71 |
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
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What the Stock Index Calculator calculates
Projects what an investment portfolio grows to from a starting amount, regular contributions and later withdrawals, net of fund costs, and splits the result into money paid in and investment growth.
How to use this Stock Index Calculator
Enter Amount invested today, Expected annual return, Compounding periods a year and Years invested. Ending balance updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Ending balance, Investment growth and Total contributed.
The method follows Lump-sum compound growth, FV = P(1 + r/n)^(nt), with growth = FV - P, US Securities and Exchange Commission (Investor.gov) - Compound Interest Calculator and Investment Company Institute, Trends in the Expenses and Fees of Funds, 2024.
What you can compare
Change one input at a time to see how it affects Ending balance, Investment growth and Total contributed. The inputs you can vary are Amount invested today, Expected annual return, Compounding periods a year, Years invested, Annual fund cost (expense ratio) and Regular contribution.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
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Frequently asked questions
How to calculate the S&P 500 index?
Projects what an investment portfolio grows to from a starting amount, regular contributions and later withdrawals, net of fund costs, and splits the result into money paid in and investment growth. Open “How this is worked out” beside the result to see each step for your own figures.
What information do I need for the Stock Index Calculator?
You need Amount invested today, Expected annual return, Compounding periods a year, Years invested, Annual fund cost (expense ratio), Regular contribution, Contribution frequency and Contributions are made. The page opens with default figures that give ending balance of 37,696.71, so you can see the scale before entering your own.
What does this Stock Index Calculator show?
It shows Ending balance, Investment growth, Total contributed, Total withdrawn, Total paid in, Effective annual return, Money-weighted annual return and Ending balance in today's money, with the working and any warnings for your entries.
Can I check how the Stock Index Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.