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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.
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.