The VOO Investing Experiment: Testing 3 Common Assumptions
Three investing beliefs tested on VOO's real prices: starting earlier, lump sum vs monthly, and waiting for a dip, plus how much the assumed return matters.
In this article
Three common beliefs, tested on VOO's real month-end prices with dividends reinvested, through 2026-11-13. Starting five years earlier with $300 a month ended at $176,523 against $79,801. A lump sum beat spreading the same money over 10 years. And waiting for a 10% dip before investing beat investing straight away in 21% of the 134 start months tested. These are past results over one stretch for U.S. stocks; they don't predict the next one.
Experiment 1: Does starting five years earlier matter?
$300 at every month-end, no starting amount, both ending at the latest month:
| Started | Put in | Worth on 2026-11-13 |
|---|---|---|
| Nov 2011 | $54,300 | $176,523 |
| Nov 2016 | $36,300 | $79,801 |
The extra five years added $18,000 of contributions and $96,723 of value. Most of the gap isn't the extra money: it's that the early contributions compounded for longer.
Experiment 2: Lump sum vs monthly, the same money
$36,000 invested at the end of Nov 2016, against $300 at every month-end from then on:
| Approach | Put in | Worth on 2026-11-13 |
|---|---|---|
| Lump sum | $36,000 | $145,061 |
| $300 a month | $36,300 | $79,801 |
The lump sum came out ahead because all of it was invested from the start of a rising decade. Most people don't have a lump sum waiting, though: investing each month is how saving from a paycheck works. The backtest calculator runs this comparison for any start month.
Experiment 3: Should you wait for a dip?
Many investors hold off until the market falls, or until it reaches a bank's year-end S&P 500 price target. Those targets are model-based estimates, and firms routinely publish different ones for the same year, so they don't tell you when to buy. To test waiting directly: for each start month from Oct 2010 to Nov 2021, compare investing $10,000 that month with waiting until VOO closed 10% lower and investing then.
- Waiting ended with more money in 28 of 134 start months (21%).
- In 106 of them the 10% dip never came, so the money would still be sitting in cash.
Waiting also costs compounding time. In a projection of $500 a month at an assumed 7%, starting now and investing for 20 years ends at $253,768; waiting a year and investing for 19 ends at $231,381, $22,387 less for $6,000 less contributed.
Run your own version of these experiments
Pick any start month and amount, lump sum or monthly, and see what VOO actually did.
Open the VOO Backtest CalculatorExperiment 4: How much does the assumed return change a projection?
For a forward-looking plan, the return you assume matters more than any other input. $300 a month for 20 years:
| Assumed annual return | Value after 20 years |
|---|---|
| 5% | $121,741 |
| 7% | $152,261 |
| 10% | $215,478 |
All three put in $72,000. Try your own in the VOO compound interest calculator.
What these experiments don't prove
VOO's data only starts in 2010, and the years since were mostly good for U.S. large companies. In a long flat or falling stretch, waiting or spreading money out can come out ahead. The results ignore taxes, trading costs and interest on cash. This is educational information, not personalized financial advice.
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This is an educational calculator, not financial advice.
Results shown are estimated future values based on the return assumption you enter — they are not predictions and VOO is not guaranteed to achieve any particular return. Past performance of the S&P 500 or any fund does not guarantee future results. Consider speaking with a licensed financial professional before making investment decisions.