Compound growth on a lump sum plus regular contributions, year by year.
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Compare robo-advisors →This is the same compound growth math behind most retirement and brokerage projections: your initial investment grows on its own, and each monthly contribution starts compounding from the moment it's added. The chart shows the total value line against a dashed line of contributions alone, so you can see how much of the final number is growth versus money you put in.
Because growth compounds on itself, the gap between the total-value line and the contributions-only line widens faster in later years than earlier ones. This is why starting earlier — even with smaller amounts — often outperforms starting later with larger contributions, given the same return rate.
Investment fees, taxes on gains, and market volatility aren't modeled — this shows a smooth average return, while real markets move up and down year to year.
Broad stock market index funds have historically averaged around 8-10% annually before inflation over long periods, though any given year can vary widely, including negative years. Bond-heavy or more conservative portfolios typically assume lower numbers.
Slightly — contributing earlier in the month gives that money a few extra days to compound versus contributing at month's end, but the difference is small compared to the impact of contributing consistently at all.
That curve is compounding in action — each year's growth is calculated on a larger balance than the year before, since prior growth stays invested and earns its own returns.