At age 1 put in $1 a day. At age 2 put in $2 a day. Keep going until today. This page runs that plan through the real S&P 500, day by day, since 1927.
The Vanguard view assumes a 0.03% annual expense ratio (the VOO ETF; the VFIAX mutual fund charges 0.04%), held constant, with dividends reinvested and no taxes. Vanguard's S&P 500 fund started in 1976 and the ETF in 2010, so earlier years show what the fund would have earned. Fees were higher in the past, so older results run slightly optimistic.
Every calendar day counts. Money for weekends and market holidays goes in at the next close. Figures are in nominal dollars, before taxes, fees and inflation. Past returns do not predict future returns, and this is an illustration, not financial advice.
Invest Your Age is an independent site. It is not affiliated with, endorsed by or sponsored by Vanguard. Vanguard, VOO and VFIAX are trademarks of The Vanguard Group, Inc., used here only to describe the fund being modeled.