How to start.
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01
Decide the destination once
Buffett's will specifies low cost, S&P 500, index. Whatever you land on, land on it once, so the monthly transfer never becomes a fresh decision.
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02
Automate on payday
Standing order, the day the money arrives. Buy before the cash has time to turn into an opinion about where the market goes next.
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03
Switch on reinvestment
Roughly 40 percent of the S&P 500's long-run total return came from reinvested dividends. Turn reinvestment on at setup, then leave it alone.
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04
Never pause on red
Falling markets are when people stop contributing. That turns a mechanical habit back into a timing call, which is what the 1.2 point gap measures.
Why it works.
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Compounding
The US stock market has returned roughly 10 percent a year on average since 1926, so money invested early spends the most years compounding at that rate.
Dimensional Fund Advisors, The Uncommon Average (1926 to 2018 data)
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Beats cash
Over 1976 to 2022, US stocks outperformed 3 month Treasury bills 76 percent of the time and bonds beat them 68 percent of the time, so holding cash carries a real opportunity cost.
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Closes gap
Over the decade to December 2024 the average dollar in funds earned 7.0 percent a year versus the funds' own 8.2 percent, a 1.2 point gap costing investors about 15 percent of total returns.
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Beats waiting
Even when it loses to lump sum investing, cost averaging still outperformed sitting entirely in cash 69 percent of the time, so a monthly habit beats waiting for a better entry point.
Who swears by it.
John's take.
Let me clear up the stat that gets thrown at this habit constantly, because almost everyone quoting it has it backwards. You’ve probably seen that Vanguard found lump sum investing beats dollar cost averaging about two thirds of the time, usually offered as proof that investing monthly is the amateur option. Read the actual paper. It compares two ways of deploying a windfall you already hold: put the whole inheritance in today, or feed it in over the next twelve months. That’s the entire question it answers.
If you’re investing 500 dollars out of every paycheck, you have no lump sum. You have a stream. You’re buying as soon as the money exists, which is precisely what that research recommends doing. There’s no strategy being chosen and nothing being given up. The comparison simply doesn’t apply to you, and the only time it will is the day a bonus or a house sale or a business exit lands in your account. That day, the finding is worth remembering: spreading a windfall out over a year is expected to cost you, and Vanguard’s own advice is to cost average only if loss aversion would otherwise leave the money sitting in cash forever. Cost averaging still beat cash 69% of the time, so it’s a fair price for staying invested. Just know what you’re buying.
The real enemy was never strategy anyway. Morningstar measured a 1.2 percentage point annual gap over the decade to 2024 between what funds returned and what the average dollar inside them actually earned, roughly 15% of total returns, gone. That gap is pure timing: piling in after the good years, flinching after the bad ones. A standing order takes you out of the loop, and the one rule I hold hard is that I don’t touch it when the screen is red, because that’s the exact moment a system quietly turns back into a guess. Running a business makes this harder than it sounds, by the way. My income is lumpy, so some months the transfer stings. It goes anyway. That’s the whole habit.
Common questions.
Is investing monthly the same as dollar cost averaging?
Not in the sense the research means, and the confusion costs people money. Vanguard's comparison is about deploying a lump sum you already hold, like an inheritance or a bonus. Investing each month as income arrives means buying as soon as you have the money, which is what Vanguard recommends. You aren't choosing a strategy, you're just not delaying.
Is dollar cost averaging worse than lump sum investing?
That question only applies to a windfall. When deploying a lump sum you already have, investing it at once beat spreading it out roughly two thirds of the time, because markets rise more often than they fall. If you're investing out of a paycheck, there's no lump sum, so the comparison isn't about you.
What should I do with a bonus or an inheritance?
This is the one case where the research bites. Spreading a windfall out is expected to cost you return, since lump sum won about two thirds of the time. Vanguard suggests cost averaging only for investors whose loss aversion would otherwise leave the money in cash entirely, and even then, cost averaging beat holding cash 69 percent of the time.
What average return should I expect from investing monthly?
The long-run US market average is about 10 percent nominal since 1926, closer to 7 percent after inflation. Plan on the real number, not the headline one. And that average almost never shows up in a given year: annual returns landed between 8 and 12 percent in only 6 of the 93 calendar years from 1926 to 2018.
Should I stop investing when the market drops?
Pausing contributions in a downturn is the most common way people convert a mechanical habit back into a timing decision. That's exactly what the 1.2 percentage point gap between fund returns and investor returns measures, and it cost investors around 15 percent of total returns over the decade to December 2024.
Do reinvested dividends really matter that much?
Roughly 40 percent of the S&P 500's long-run total return has come from reinvested dividends, so reinvestment should be switched on by default. Bogle's argument was the mirror image of the same force: costs compound against you exactly as returns compound for you, which is why he founded Vanguard in 1974 and launched the first retail index fund.