How this dollar-cost averaging calculator works
This calculator separates two things every other DCA tool conflates: how long you actually spread a windfall out (the deployment period — realistically 6-12 months, not years), and how far out you want to forecast the result (the total time horizon — years or decades). Set your amount, schedule, and deployment window, plus two return assumptions: the expected annual return (treated as the long-run compound growth rate) and the annual volatility (how violently returns swing around that average). The calculator simulates 500 possible markets with those characteristics; DCA contributes on schedule until the deployment window ends, then simply holds — exactly like the lump sum has been doing since day one — all the way out to your chosen horizon. The median path is shown in yellow with a shaded band covering the 10th to 90th percentile of outcomes, and the stepped grey line is your cost basis — money in — which flattens out once deployment finishes.
The lump-sum toggle answers the question every DCA calculator dodges: what if you'd invested the same total on day one? The comparison is honest because both strategies face the identical 500 simulated markets — same crashes, same rallies, only the timing of your money differs — and both are then held for the same total horizon, so you can see whether an early timing edge (or setback) persists, fades, or compounds over the years that follow. The duel bar above the chart shows both median outcomes side by side, along with how often each strategy won.
What dollar-cost averaging is
Dollar-cost averaging means investing a fixed dollar amount on a fixed schedule — $500 every month, rain or shine — instead of trying to pick moments. The mechanism that makes it interesting is arithmetic, not magic: a fixed amount buys more shares when prices are low and fewer when prices are high. Over a volatile stretch, your average cost per share ends up below the average of the prices you bought at (the harmonic mean sits under the arithmetic mean). You didn't predict anything; the fixed dollar amount did the timing for you, automatically leaning into weakness and away from froth.
It's worth separating true DCA from what most people actually do. Investing part of every paycheck — a 401(k) contribution, an automatic monthly transfer — looks like DCA but is really just investing money as fast as it arrives, which is optimal. The genuine DCA decision only appears when you're holding a pile of cash — an inheritance, a bonus, a home-sale windfall — and must choose between deploying it all now or spreading it out.
When DCA helps, and when it hurts
DCA wins when prices fall or chop sideways during your deployment window: every purchase after a decline lowers your average cost, so a partial recovery is enough to put you in profit. It also wins behaviorally — an automated schedule removes the temptation to wait for a better entry that never comes, and it caps the damage of catastrophically bad timing. The 10th-percentile numbers in the table below are where that insurance shows up.
DCA hurts when markets rise during the deployment — which, historically, is most of the time. Money sitting in cash waiting for its scheduled entry misses growth, and with a positive expected return, the earlier a dollar is invested the more it's expected to earn. That's the whole case for the lump sum, and it's a strong one.
The lump-sum-usually-wins nuance
Vanguard's research made the short-window version famous: spread a lump sum over 6–12 months and the day-one deployment ends higher in roughly two-thirds of markets. This calculator's own default — a $60,000 windfall deployed over 12 months, both strategies then held out to a 10-year horizon — lands at almost exactly that figure: the lump sum wins about 67% of simulated markets. That's the realistic comparison, because a 12-month deployment window is what people actually mean by "should I DCA my windfall." Stretch the deployment window itself out to a decade — $500 a month for 10 years instead of a real windfall spread over months — and the win rate for the lump sum climbs toward 90%, but at that point you're not really comparing DCA-vs-lump-sum anymore; you're comparing "having the money now" against "earning and saving it gradually over 10 years," which is a different question with an obvious answer (money in hand is better than money you haven't earned yet). The deployment-period field above is deliberately capped for that reason — realistic windfall timing decisions live in the 6-12 month range.
Expected value favors immediacy; that's not a quirk of this calculator, it's the arithmetic of markets that rise more years than they fall. So why does DCA survive as advice? Because the average hides the tails. At the realistic 12-month deployment window, DCA's worst-case (10th percentile) outcome is genuinely better than the lump sum's worst case — real downside protection, not just a smaller number. The investor who panic-sells after seeing a windfall crater has turned a temporary loss into a permanent one, and DCA's genuine contribution is making that scenario rarer. The honest framing: lump sum maximizes expected wealth; DCA minimizes expected regret, and that trade-off is real and worth roughly a coin flip's worth of odds against you, not a near-certainty. Pick based on which failure you're more likely to commit, then automate the choice and stop looking. Whichever way you deploy, the destination matters more than the entrance: the multi-phase compound interest calculator models the decades after the money is in, and the Coast FIRE calculator shows when those steady contributions have already done enough that you could stop making them.
Frequently asked questions
What is dollar-cost averaging?
Investing a fixed dollar amount on a fixed schedule regardless of market conditions. The fixed amount automatically buys more shares when prices are low and fewer when they're high.
Does DCA beat lump-sum investing?
Usually not — a day-one lump sum wins roughly two-thirds of the time because markets rise more often than they fall. DCA wins in falling markets and meaningfully softens worst-case outcomes.
How often should I invest?
Weekly, biweekly, or monthly barely differ in the long run. Monthly matches most paychecks. Consistency beats frequency — the schedule you'll actually stick to is the right one.
Is paycheck investing the same as DCA?
Mechanically yes, but conceptually it's rolling lump-sum investing — you're deploying money as fast as you get it, which is already optimal. True DCA is choosing to spread out cash you already hold.
What volatility should I enter?
~15% for a diversified stock index, ~9–10% for a 60/40 portfolio, 20%+ for aggressive or concentrated portfolios. Zero shows the flat-rate fantasy most calculators present.
How does the volatility modeling work?
500 Monte Carlo simulations draw random per-interval returns from a log-normal distribution calibrated to your return (as CAGR) and volatility. Both strategies face the same 500 markets, and a fixed seed keeps results reproducible.
Is DCA good in a bear market?
It's where DCA shines — each purchase lowers your average cost, so a smaller recovery reaches break-even. The catch is that bear markets are only obvious in hindsight, which is why the schedule matters.
Does DCA reduce risk?
It reduces timing risk during deployment — narrower outcomes, better worst case, worse best case. It does nothing about market risk after you're fully invested.
What's the cost basis line?
Total money contributed so far, before growth — the stepped grey line on the chart. Value above it means profit; below means underwater.
Should I DCA a windfall?
Math says invest it now; psychology often says spread it over 6–12 months. If a 20% drop the week after investing would make you panic-sell, DCA's insurance is worth its expected cost.
Why does the lump sum usually win here?
It puts all the money to work on day one, while DCA's later contributions sit in cash first. At a realistic 6–12 month deployment window, that's worth roughly two-thirds of simulated markets, no matter how far out you forecast afterward. Check the 10th percentiles to see DCA's side of the trade.
Does DCA work for crypto or single stocks?
The mechanics work on anything with a price, and higher volatility strengthens the timing-risk argument. But DCA can't rescue a bad asset — averaging into something that goes to zero is just losing money in installments.
This calculator is for education, not investment advice. Simulated markets are simplified models — real returns include fat tails, momentum, and correlations no log-normal distribution captures. Confirm decisions with a qualified advisor.