About dollar-cost averaging
Dollar-cost averaging (DCA) means investing a fixed amount on a regular schedule, for example $500 every month, regardless of whether the market is up or down. When prices are low your fixed sum buys more shares, and when prices are high it buys fewer, so your average cost per share is smoothed over time. It is the mechanism behind every 401(k) and automatic index-fund contribution, and it removes the temptation to time the market.
This calculator projects the future value of a DCA plan from your starting balance, monthly contribution, time horizon, and expected return. It is important to separate two questions DCA often gets confused between. As a way to invest a windfall, DCA historically underperforms investing the lump sum immediately about two-thirds of the time, because markets rise more often than they fall. But as a way to invest money you earn gradually from each paycheck, DCA is simply the optimal and only realistic approach, and its real value is behavioural: it enforces discipline and removes emotion.
How it works
The projection grows the starting balance and the stream of monthly contributions at the expected rate of return. The contributions form an ordinary annuity, so their future value uses the annuity formula:
FV = init x (1 + r)^n + monthly x ((1 + r)^n - 1) / r init = initial investment monthly = recurring contribution r = periodic (monthly) return = annual return / 12 n = number of contributions (months)
- The first contribution compounds longest, so early deposits matter most to the final balance.
- Return is the biggest lever over long horizons, but it is also the least controllable; contribution amount is what you actually decide.
- Volatility does not change the expected end value in this model, but in reality it affects the path and your behaviour along the way.
Worked example
An investor starts at $0, contributes $500 a month for 20 years, and assumes a 7 percent annual return.
- Monthly return: 7 percent / 12 = about 0.583 percent.
- Months: 20 x 12 = 240 contributions.
- Total contributed: $500 x 240 = $120,000 of your own money.
- Future value: the annuity formula gives roughly $260,000.
- Growth: about $140,000, more than the amount contributed, all from compounding.
DCA outcomes by horizon
Approximate future value of $500 per month at 7 percent annual return, starting from zero.
| Years | Total contributed | Approx. future value | Growth |
|---|---|---|---|
| 10 | $60,000 | ~$86,000 | ~$26,000 |
| 20 | $120,000 | ~$260,000 | ~$140,000 |
| 30 | $180,000 | ~$606,000 | ~$426,000 |
| 40 | $240,000 | ~$1,310,000 | ~$1,070,000 |
Lump sum versus dollar-cost averaging
If you receive a windfall, an inheritance, a bonus, or proceeds from a sale, the question is whether to invest it all at once or feed it in over months. Vanguard's well-known study found that investing a lump sum immediately beat spreading it over twelve months about two-thirds of the time across US, UK, and Australian market history. The reason is simple: markets spend more time rising than falling, so money sitting on the sidelines usually misses gains rather than dodging losses. On average, lump sum investing led to higher ending balances.
The case for spreading a windfall is behavioural, not mathematical. If investing everything at once and then watching a sharp drop would frighten you into selling, then averaging in over a few months buys peace of mind and reduces regret risk, at the cost of slightly lower expected returns. For the money you earn from each paycheck, though, there is no lump sum to compare against: contributing it as it arrives is dollar-cost averaging by necessity and is exactly the right thing to do.
Common pitfalls
- Confusing the two uses of DCA. Spreading a lump sum over time usually lags investing it all at once; investing each paycheck as it arrives is just sensible investing.
- Stopping during downturns. The whole edge of DCA comes from buying more shares when prices are low, so pausing in a crash defeats the strategy.
- Assuming a smooth 7 percent. Real returns are lumpy; the model shows the expected path, not the bumpy reality.
- Ignoring fees and inflation. Expense ratios and rising prices both eat into the real, after-cost outcome.
- Underrating the behavioural benefit. The biggest gain of automatic DCA is that it keeps you invested and contributing through every market mood.
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Frequently asked questions
What is dollar-cost averaging?
Dollar-cost averaging is investing a fixed amount on a regular schedule, such as $500 every month, no matter what the market is doing. When prices fall, your fixed sum buys more shares; when they rise, it buys fewer. This smooths your average purchase price over time and removes the need to guess when to buy.
Is dollar-cost averaging better than investing a lump sum?
For investing a windfall, no, not usually. Historically, investing a lump sum immediately beats spreading it out about two-thirds of the time, because markets rise more often than they fall. But for money you earn gradually from each paycheck, DCA is the natural and optimal approach, and its real strength is behavioural discipline.
How is the future value of a DCA plan calculated?
It uses the annuity future-value formula: FV = init x (1+r)^n + monthly x ((1+r)^n - 1) / r, where init is the starting balance, monthly is the recurring contribution, r is the monthly return (annual return divided by 12), and n is the number of monthly contributions. The starting balance and each contribution compound to the end of the horizon.
Why does DCA work better over long horizons?
Because the earliest contributions have the most time to compound. Over 10 years $500 a month at 7 percent grows to about $86,000, but over 30 years the same monthly amount grows to roughly $606,000. Most of that difference is compounding on the early deposits, which is why starting sooner matters more than contributing more later.
Should I stop dollar-cost averaging when the market drops?
No. Market downturns are when a fixed contribution buys the most shares at the lowest prices, which is exactly the advantage DCA is designed to capture. Pausing during a crash means missing those cheap purchases. Staying consistent through every market mood is the behavioural benefit that makes automatic DCA effective.