Index Fund Calculator

An index fund does not attempt to select securities; it reproduces the composition of a published benchmark, holding each constituent at its index weight and trading only when the index itself is reconstituted. That mechanical mandate is what makes the return modellable: the expected gross return is the benchmark return, and the investor's realised return is the benchmark minus the expense ratio and minus tracking difference. This projection uses that structure directly, subtracting the expense ratio from the assumed annual return before compounding monthly on both the opening lump sum and the recurring contribution. Turnover in a broad index fund typically runs around 3 to 5 percent a year against 50 to 100 percent for an active fund, which is why index products also distribute fewer taxable capital gains in a taxable account. The reference numbers behind the default inputs are worth stating precisely. The S&P 500 has returned roughly 10 percent a year nominal over the long run and about 7 percent after inflation, but the dispersion around that average is enormous: the decade to 2010 was close to flat in nominal terms while the decade to 2020 exceeded 13 percent. The inflation field matters as much as the return field, because real return is (1 + net return) / (1 + inflation) - 1, not the difference of the two. A projection that ends at a million nominal dollars in 30 years is worth roughly 412,000 dollars in current purchasing power at 3 percent inflation. Constant-rate models also hide sequence risk entirely.

Indexing began as a theoretical argument before it was a product. Harry Markowitz set out portfolio selection in 1952, William Sharpe derived the capital asset pricing model in 1964, and Eugene Fama formalised the efficient market hypothesis in 1970 - together implying that the market portfolio was a defensible holding for an investor with no informational edge. Paul Samuelson pressed the practical case in his 1974 essay Challenge to Judgment, effectively daring some institution to build a fund that simply tracked the market. Institutions moved first. Wells Fargo's trust department constructed an equal-weighted New York Stock Exchange index account for the Samsonite pension fund in 1971, and American National Bank and Batterymarch launched comparable vehicles for institutional clients over the following years. The retail version came from John Bogle, who launched the First Index Investment Trust at Vanguard on 31 August 1976. Its underwriting raised only about 11 million dollars against a 150 million dollar target and Wall Street nicknamed it Bogle's Folly, but the fund - later renamed the Vanguard 500 Index Fund - grew into one of the largest in the world. Evidence accumulated in its favour: S&P Dow Jones Indices has published the SPIVA scorecard since 2002, and its long-horizon results repeatedly show the large majority of active large-cap managers trailing their benchmark over fifteen years.