What return is realistic?

The S&P 500's long-run average is around 7–10% before inflation, but any single decade can be much higher or lower. Model conservatively.

How much do fees matter?

Enormously over time. A 1% annual fee can consume a large share of your gains over decades — index funds are popular precisely because their fees are tiny.

Index Fund Calculator

Project long-term growth of regular index-fund contributions.

UPDATED · MAY 2026

Initial investment

Monthly contribution

$/mo

Years invested

Expected return

S&P 500 long-run avg ≈ 7–10%

After 30 years at 8%

$556,465

INVESTED$118,000

MARKET GAIN$438,465

Future value

$556,465

Total invested

$118,000

Gain

$438,465

INDEX FUND GROWTH

Total value Invested

How to use the Index Fund Calculator

01
Enter your initial investment. Your starting lump sum, if any.
02
Add a monthly contribution. Regular deposits compound alongside it.
03
Set years and expected return. The S&P 500 has averaged roughly 7–10% long-term.

How is it calculated?

We compound your initial investment and each monthly contribution at your expected annual return, monthly, over the chosen period. Index funds work because of low fees and broad diversification — over decades, steady contributions plus compounding turn modest monthly amounts into large balances.

Frequently asked

The questions readers ask most about the index fund calculator.

Index funds spread risk across hundreds of companies at very low cost, and most actively managed funds fail to beat the index over the long run.

LEARNCompound interest explained: how money grows over time

How to use the Index Fund Calculator

How is it calculated?

Frequently asked

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