Index Fund Calculator

Project index fund growth with low expense ratio vs managed fund comparison.

By Konstantin Iakovlev · Updated September 2026 · Source: SEC

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Index Fund Value

$1.1M

Managed Fund Value

$915.4K

Fee Savings

$207.7K

Comparison

Total Contributed$180,000.00
Index Fund (0.03% ER)$1.1M
Managed Fund (1.00% ER)$915.4K
Extra from Low Fees$207.7K

Use the Index Fund Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Fees are quiet, but over decades they are anything but small. Comparing a low-cost index fund against a traditional actively managed fund here makes that gap visible, showing how a fraction of a percent in expense ratio can split into a wide gulf in ending wealth over a working lifetime.

The projection runs on a compound interest formula that takes in your monthly contribution, the expected annual return, the number of years and the expense ratio of the index fund, set against a 1.00% expense ratio for the managed fund. The future value is computed as FV = PMT × [((1 + r/12)^(12t) − 1) / (r/12)], where 'r' is the net annual return, that is the gross return minus the expense ratio. Running both funds through it produces a clean comparison of growth after fees are taken out.

The numbers are projections, not promises, since past performance never guarantees what comes next. Many investors fixate on headline gross returns and miss how steadily high fees erode a balance over the long haul. Taxes also matter to your real outcome, though this particular calculation leaves them out.

Example: $500 a month for 30 years

  1. 1 You invest $500 a month for 30 years ($180,000 in total) and assume a 10% gross annual return for both funds: an index fund charging 0.03% and an actively managed fund charging 1.00%.
  2. 2 Net of fees the index fund compounds at 9.97% and the managed fund at 9.00%, each applied monthly to the growing balance.
  3. 3 After 30 years the index fund is worth about $1,123,037 and the managed fund about $915,372. The 0.97-point fee gap costs $207,665, more than the $180,000 you put in.
  4. 4 This example clearly illustrates how even a seemingly small difference in expense ratios compounds over time. Over longer periods, this gap widens dramatically, highlighting why prioritizing low-cost index funds is a cornerstone of effective long-term investing.

Source: SEC · Last updated: September 2026

Frequently Asked Questions

How much should I invest in index funds?
Many financial advisors recommend index funds as the core of your portfolio (60-90% of stock allocation). The amount depends on your goals, timeline, and risk tolerance. Even $100/month invested in a broad market index fund grows significantly over decades due to compounding.
What is a good expense ratio for an index fund?
Top index funds charge 0.03-0.10% annually. Anything below 0.20% is good. Avoid funds charging above 0.50% for passive indexing. With the calculator's defaults, $500 a month for 30 years at a 10% gross return, the gap between a 0.03% and a 1% expense ratio is $207,665.
Do index funds outperform managed funds?
Over 15+ year periods, roughly 85-90% of actively managed funds fail to beat their benchmark index after fees. Low-cost index funds provide broad diversification and consistently strong long-term returns, which is why they are recommended for most investors.

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