Estimate long-term growth in an index-fund scenario, including an annual expense assumption. An index fund follows a specified benchmark; the benchmark could represent equities, bonds or another market. A low fee alone does not describe the investment’s risk.
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Before you enter your numbers
Choose a return assumption for the benchmark exposure you actually intend to model. A broad equity assumption should not be used unchanged for a short-duration bond index. Enter contributions that can be maintained through market declines, not just during strong performance.
- Starting investment
- Monthly contribution
- Years
- Gross annual return
- Expense ratio
Input reference
- Starting investment: The current balance committed to this goal. Use a recent statement and exclude money reserved for unrelated goals. This starting value is already invested, so do not also enter it as a recurring contribution.
- Monthly contribution: New money added at the end of each month. Convert annual saving to a monthly amount by dividing by 12. This page does not schedule skipped months or one-time deposits automatically.
- Years: The duration of the calculation in years. Longer periods give growth or withdrawals more time to operate. This is a chosen modeling horizon, not a prediction of an investment term or your lifetime.
- Gross annual return: An assumed nominal annual rate, divided by 12 in monthly projections. It is held constant. It is not a guaranteed yield, and the default should be replaced with an assumption suited to your scenario.
- Expense ratio: An annual percentage-point deduction from the gross return assumption. Check whether the source return already deducts this fee. One-time charges, trading costs and fixed account fees are not modeled by this field.
Formula and calculation method
The model subtracts the expense ratio from the annual return and compounds monthly. This approximates cost drag while leaving contributions unchanged. If your starting return is already net of fund expenses, avoid deducting the same expense again.
Worked example
At 6% gross return with a 0.2% annual expense ratio, the model uses 5.8%. A comparison fund with a 0.7% expense ratio uses 5.3% under the same gross assumption. Hold the investment period and contributions constant to isolate the modeled fee effect.
How to interpret the result
The result shows the projected ending value after the entered fund expense ratio, alongside total contributions and estimated growth. It is a constant-return scenario for one index fund, not a backtest of a particular benchmark.
Tracking difference can include more than the headline expense ratio. Sampling, taxes, cash holdings and implementation can also affect returns relative to the benchmark. This page does not model those items separately or guarantee that the fund will match the index.
Index-fund return after fees
The projection starts with the gross return assumption and subtracts the fund expense ratio before compounding. It then adds regular monthly investments so you can separate total invested capital from estimated market growth.
Tracking error, taxes and transaction costs are not modeled. If you are comparing real funds, use the published expense ratio and remember that index funds following different benchmarks can have very different risk and return profiles.
Benchmark choice comes before fee comparison
A domestic large-company index and a global stock index have different exposures. A lower expense ratio does not make them interchangeable. Compare costs among suitable funds only after understanding what the benchmark holds and how it fits with the rest of your portfolio.
A market-cap-weighted index may become concentrated in its largest constituents. Owning many securities does not guarantee even exposure across companies, countries or sectors. The projection does not inspect holdings or concentration; it treats your return assumption as a single constant rate.
Include the fund cost and use a return assumption that fits the index
Index funds can track very different markets, so the words “index fund” do not imply one expected return. A broad stock index, bond index and short-term Treasury index have different risk and return characteristics. Use an assumption aligned with the specific exposure being modeled.
If the calculator includes fees, use the current expense ratio and avoid entering a return that is already net of that same fee. Taxes and tracking difference may also reduce the investor’s realized result outside tax-advantaged accounts.
Use The Result In The Next Calculation
Use the result to see how contributions and the entered expense ratio affect a long-term index-fund scenario. If you need a multi-asset allocation, switch to the portfolio calculator rather than averaging unrelated assets into one index-fund return.
Retirement planning guides · Calculation methodology
Rules and limits can change. Use these primary sources to verify time-sensitive details.
Index Fund Calculator FAQs
Is an index fund the same thing as an ETF?+
No. Indexing is an investment approach; ETF is a fund structure. An index strategy can be offered through an ETF or a mutual fund, and some ETFs are actively managed.
Where can I check the assumptions behind this result?+
Check the formula and limitations sections on the Index Fund Calculator page for the assumptions specific to this tool. The methodology page explains conventions shared across calculators, and Investor.gov fund resources is the reference for any time-sensitive statutory or product rule mentioned here.
What does the Index Fund Calculator result include?+
It includes the starting balance, monthly deposits, gross return assumption and the entered index-fund expense ratio. It does not retrieve a live index level or reproduce the historical path of a named fund.
What should I change when testing another Index Fund Calculator scenario?+
Change one input at a time: contribution amount, years, gross return or expense ratio. That makes it clear whether the result changed because you saved more, invested longer or assumed a different fund cost or return.
Can the Index Fund Calculator replace an official statement or professional advice?+
No. It is a planning calculator. Index funds track different indexes and carry different risks. An assumed return should match the type of fund you are modeling. Use official statements and current rules when an exact legal, tax, pension or account figure is required.