Free · Expense ratios · Boglehead-friendly

Index fund calculator

Project growth of a total-market or S&P 500 index fund over decades. Set your expected return after fees and see exactly how compounding builds wealth on autopilot.

Index fund expense ratios that matter · Vanguard, Fidelity, Schwab prospectuses · Morningstar Active/Passive Barometer

Total-market index ER: 0.02%–0.04% · target-date 0.08%–0.15%

VTSAX/VTI sits at 0.03%, FZROX at 0%, SWTSX at 0.03%. The historical 'average expense ratio' figure of 0.5%+ is dominated by actively managed funds — passive index funds have effectively zero cost at the major brokerages now.

We default the ER input to 0.03% because most calculators still assume a fictional '0.50% average' that hasn't reflected real index fund pricing since 2018.

Expense ratios — the silent drag

Every index fund charges a small annual fee, expressed as the expense ratio. It's tiny but compounds against you for decades. To project net returns, subtract the expense ratio from your assumed gross return.

VTSAX / VTI (Vanguard Total Stock): 0.04%
FXAIX (Fidelity S&P 500): 0.015%
SWPPX (Schwab S&P 500): 0.02%
Average actively managed mutual fund: 0.65%

On $500k over 30 more years, going from 0.04% to 0.65% costs roughly $135,000 in foregone growth. Pick the cheapest broad index fund you can.

What return assumption should I use?

S&P 500 1928–2025 nominal: ~10% with dividends reinvested
S&P 500 real (after inflation): ~7%
Total US Stock Market (VTSAX): ~9.5% nominal long-term
60/40 stock/bond portfolio: ~7% nominal, 4% real

$500/month in a total-market index fund

Years	7% real	9% nominal	10% nominal
10	$86k	$96k	$102k
20	$259k	$330k	$378k
30	$606k	$905k	$1.13M
40	$1.30M	$2.25M	$3.16M

Index Fund Calculator FAQ

Which index fund should I pick?

A total US stock market fund (VTSAX, VTI, FSKAX) or an S&P 500 fund (VOO, FXAIX, SWPPX) — all with expense ratios under 0.05%. For full global exposure, add a total international fund (VXUS, FTIHX) at 20–30% of equities. That's the entire portfolio for most Bogleheads.

Is the S&P 500 going to keep returning 10%?

Nobody knows. 10% is the nominal long-run average from 1928 to today. There are decades that returned 18% and decades (1929–1939, 2000–2009) that returned near zero. Plan conservatively with 7% real and you'll be roughly right over 20+ year horizons.

How does this calculator handle dividends?

It assumes total return — dividends are reinvested back into the fund. Real-world index funds in an IRA or 401(k) auto-reinvest by default. In taxable accounts, dividend distributions are taxed at qualified rates (0–20%) the year they're paid.

Index funds vs ETFs — same thing?

Functionally yes, structurally a bit different. Mutual fund index versions (VTSAX) settle once daily at NAV. ETF versions (VTI) trade like stocks throughout the day. ETFs are slightly more tax-efficient in taxable accounts due to the in-kind redemption mechanism. Same underlying holdings.

Should I time the market with index funds?

No. Decades of data show lump-sum investing beats waiting ~70% of the time, and dollar-cost averaging beats timing attempts. The cost of being out of the market on the 10 best days per decade can cut returns by 50%+. Buy and hold, rebalance once a year.

What about index fund crashes?

Total-market and S&P 500 indexes have drawn down 50%+ multiple times (2000–2002, 2008–2009, 2020) and recovered every time. The key is staying invested. The calculator's smooth curve hides this — assume your real path has stomach-turning dips and a long-term upward slope.

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Index funds + savings rate = FIRE.

Methodology, sources, and editorial standards

The index fund calculator on this page uses the same closed-form math published by the U.S. Securities and Exchange Commission's consumer-investor portal at Investor.gov and the Consumer Financial Protection Bureau. Every number you see is generated client-side in your browser — no data is sent to our servers, no account is required, and no personally identifiable information is stored or shared. The calculation assumes constant rates and contributions over the modeled period; real-world returns, fees, and tax treatment vary year to year, and the figures presented are educational projections, not personalized financial advice.

We cite primary data sources directly within the FAQs and snapshot block above. Historical return assumptions are drawn from NYU Stern's historical returns database (Aswath Damodaran) and Robert Shiller's S&P 500 dataset. Inflation comparisons rely on the Bureau of Labor Statistics CPI series. Mortgage and credit-card market data come from Freddie Mac's PMMS and the Federal Reserve's G.19 release, respectively. Where we publish our own multi-scenario research, the dataset is available under a Creative Commons CC-BY 4.0 license at snowballr.io/data.

Snowballr is an independent, ad-supported publication. We do not sell financial products, accept affiliate commissions on bank, brokerage, or loan products, or take payment for editorial placement. Our editorial standards describe how we source, fact-check, and update every calculator and guide. The full master sources index lists every primary reference used across the site, organized by topic. For corrections, updates, or fact-checking inquiries, contact us via the contact page; we typically respond within 24–48 hours.

Important disclaimer: This calculator is provided for educational purposes only. It does not constitute investment, tax, accounting, legal, or financial-planning advice and should not be used as the sole basis for any decision about your money. Compound projections, debt-payoff schedules, and retirement estimates depend on assumptions that will change in real life — investment returns are not guaranteed, market downturns can extend recovery timelines, fees and taxes reduce realized growth, and inflation erodes the real purchasing power of nominal balances. Before making a financial decision based on any number you calculate here, consult a fiduciary financial advisor, a licensed tax professional, or both, as appropriate to your situation. Past performance does not guarantee future results.

Who uses this calculator

The index fund calculator is used by three distinct audiences, each for a different question. New investors and savers use it to answer the foundational "what could this become?" question — they enter conservative monthly amounts and realistic return assumptions to see whether building meaningful wealth on a normal salary is actually possible. The answer, for almost every income level, is yes; the math just requires patience and consistency that intuition resists. Mid-career professionals use the same tool to stress-test their retirement plan against catch-up contributions, late-career raises, and the trade-off between paying down debt and investing in tax-advantaged accounts.

Pre-retirees and recent retirees use the calculator to validate withdrawal sustainability and to model what happens if a market downturn coincides with the start of retirement. Educators, financial coaches, and personal-finance bloggers use Snowballr's calculators in their teaching because every input is visible, every formula is documented, and the year-by-year breakdown lets learners see exactly where compounding pulls ahead of contributions. We support that use case explicitly under our Creative Commons license — you can embed any calculator on your own site using the snippet generator at /widgets and cite Snowballr per the citation guide.

Common assumptions and how to interpret the numbers

The output is only as accurate as the inputs and the assumptions that bridge them to real life. Three categories of assumption deserve the most scrutiny. Returns are nominal unless explicitly labeled real (inflation-adjusted); a seven-percent nominal return is closer to four-percent real, which materially changes long-horizon projections. Inflation itself averaged just under three percent in the U.S. from 1928 through 2024 but ran above five percent in roughly fifteen of those years and below zero in three. Average expense ratios for index funds dropped from roughly one-and-a-half percent in 2000 to under a tenth of a percent today, but actively managed mutual funds still average about half a percent — which translates to a quarter of the final balance lost to fees over a thirty-year horizon at typical contribution rates.

Taxes affect both contributions and withdrawals in ways the headline number does not show. Pre-tax contributions in a traditional 401(k) or IRA receive a deduction today but trigger ordinary income tax on withdrawal. Roth contributions are post-tax today but grow and withdraw tax-free. Taxable brokerage accounts pay tax annually on dividends and at sale on capital gains. If you are comparing projected balances across account types, equalize by reducing pre-tax balances by your expected retirement tax rate and adding back the dividend drag on the taxable account; otherwise the comparison is misleading. Our 401(k) vs Roth IRA comparison walks through this explicitly with worked examples at three tax-bracket scenarios.

For inputs you are uncertain about, run the calculator twice with a high and a low value to see how sensitive the answer is to your assumption. If a two-percent rate change moves the final balance by less than ten percent, the assumption is not very load-bearing. If it moves the balance by forty percent or more, that input dominates the model and deserves the most careful estimation. The single highest-leverage input in almost every compound-interest scenario is time — every additional year compounds geometrically — followed by rate, then contribution, then starting principal in roughly that order.