Is dollar-cost averaging better than investing a lump sum all at once?

Not usually, if you already have the lump sum available and markets tend to rise over time; investing it immediately has historically outperformed spreading it out in most multi-year windows. Dollar-cost averaging earns its keep mainly as a discipline for money you receive gradually, such as a salary, and as a way to reduce the regret of investing a large sum right before a downturn.

What counts as a good monthly amount to invest?

There is no universal figure; what matters is consistency relative to your income and time horizon. Someone investing 300 a month for 30 years at 7% ends with more than someone investing 400 a month for only 15 years at the same rate, so a smaller amount started early usually beats a larger amount started late.

Why does the ending balance grow so much faster in the later years?

Because interest earns interest. Early on, growth is calculated on a small balance, so it looks modest even though the percentage return is identical every year. By the second half of a long plan the balance itself has become the largest source of new growth, which is why 400 a month over 30 years produces well over double the result of the same amount over 20 years.

Does this calculator account for market crashes?

No. It compounds one constant annual rate for the entire period, so it cannot show what happens if a downturn hits early versus late in the plan, even though that timing changes the real outcome for two savers with the same average return. Use the output as a steady-state anchor, not a stress test.

Should I include my employer's 401(k) match in the monthly figure?

Yes, if you want the projection to reflect what actually lands in the account each month. A match is effectively an extra contribution on top of your own, so leaving it out understates the ending value, sometimes substantially, depending on how generous the match is.

How often should I revisit the numbers I entered?

At least once a year, and after any change to income, contribution amount, or the return assumption you are comfortable using. A projection built on a rate or a monthly amount from several years ago will drift away from reality faster than most people expect, particularly after a raise or a change in asset allocation.

Dollar-cost averaging calculator

This calculator projects a fixed monthly contribution, plus an optional starting lump sum, compounding at a steady assumed annual return. The ending value is not a forecast of what any real portfolio will do; it is a clean baseline that shows how much of the final total is money you put in versus money the market added, so you can judge whether a savings rate or a time horizon is doing enough of the work.

Reading the split between contributions and growth

Investing 400 a month at a steady 7% for 20 years produces about 208,371, built from 96,000 you contributed and about 112,371 of growth. Growth already exceeds your own money by year twenty, which is the point most long-term investing plans are aiming for.

Stretch the same 400 a month to 30 years at the same 7% and the total rises to about 487,988, from 144,000 contributed and roughly 343,988 of growth. The extra decade adds only 48,000 in contributions but more than doubles the ending balance, because compounding is working on an already-larger base for longer.

A useful benchmark: if growth is smaller than your contributions after fifteen-plus years at a normal equity-like return, either the assumed return is too conservative for the asset mix you actually hold, or the plan has not been running as long as you think.

Three scenarios worth comparing

Time horizon: 400 a month at 7% run for 20 years reaches 208,371; the same monthly amount run for 30 years reaches 487,988. Ten extra years is worth roughly 2.3 times the money for the same monthly habit, which is the core argument for starting early rather than starting big.

Lump sum plus monthly top-ups: 5,000 invested up front alongside 250 a month at 6% over 25 years reaches about 195,573, made up of 80,000 contributed and 115,573 of growth. The lump sum is a small share of the 80,000 contributed but, because it compounds for the full 25 years, it contributes a disproportionate share of the final growth figure.

Starting ten years earlier on a smaller budget: 300 a month at 7% for 20 years reaches 156,278, while the same 300 a month for 30 years reaches 365,991. The 30-year saver puts in only 36,000 more in total but ends with almost 210,000 more, which is the clearest illustration of why the years you invest matter more than the amount in most people's twenties.

What dollar-cost averaging actually smooths, and what it does not

Investing the same amount on a fixed schedule buys more units when prices are down and fewer when prices are up, which lowers the average price paid compared with buying a fixed number of units every time. What it does not do is guarantee a positive return, avoid a market decline, or beat investing a lump sum immediately when markets trend upward, which historically happens more often than they trend downward.

The 'halfway point' figure this calculator shows is a useful gut check: in a steady-return model the balance at the midpoint of the term is always well under half the final balance, because most of the growth accumulates in the second half once the base is larger. If your own portfolio's midpoint balance already looks close to half the goal, the plan is ahead of a simple steady-return path, not behind it.

Sequencing still matters even within a DCA plan. Two savers who contribute the same total amount over the same number of years can finish with different balances purely because of when the market fell relative to when their contributions were largest, something a single constant rate cannot show.

Where the steady-return assumption breaks down

Real markets do not return the same percentage every year; they compound a sequence of very different annual results that happen to average out to something like the number you typed in. Two portfolios with the same long-run average return can finish with noticeably different balances if the bad years land early instead of late, an effect this model cannot represent.

The projection also excludes fund fees, trading costs, taxes on dividends or realised gains, and any behavioural gaps such as pausing contributions during a downturn. Even a fee of half a percentage point a year, left uncorrected over three decades, quietly removes a meaningful slice of the growth line shown here.

Finally, it assumes the contribution amount never changes. In practice, raises, bonuses, and periods of reduced saving all shift the real trajectory, so treat the output as a planning anchor to revisit yearly rather than a fixed prediction to bank on.

Which account this compounding assumption actually matches

In the United States, whether growth is taxed as it happens depends heavily on the account: a traditional or Roth IRA and most 401(k) plans shelter this kind of compounding from annual tax, while a standard brokerage account does not, so the after-tax version of these numbers can be meaningfully lower outside a retirement account. IRA contributions are also capped each tax year by the IRS, which limits how much monthly investing you can shelter this way regardless of how much you can afford to save.

In the United Kingdom the equivalent shelter is an ISA, with its own annual allowance reset each 6 April, or a workplace pension, where employer contributions add to the monthly figure this calculator only lets you enter as your own input.

Automatic monthly investing inside a tax-advantaged account is usually the most literal real-world match for this model; automatic investing in a taxable account will drift below the projection over long horizons purely from tax drag, even before fees are considered.

Frequently asked questions

Is dollar-cost averaging better than investing a lump sum all at once?: Not usually, if you already have the lump sum available and markets tend to rise over time; investing it immediately has historically outperformed spreading it out in most multi-year windows. Dollar-cost averaging earns its keep mainly as a discipline for money you receive gradually, such as a salary, and as a way to reduce the regret of investing a large sum right before a downturn.
What counts as a good monthly amount to invest?: There is no universal figure; what matters is consistency relative to your income and time horizon. Someone investing 300 a month for 30 years at 7% ends with more than someone investing 400 a month for only 15 years at the same rate, so a smaller amount started early usually beats a larger amount started late.
Why does the ending balance grow so much faster in the later years?: Because interest earns interest. Early on, growth is calculated on a small balance, so it looks modest even though the percentage return is identical every year. By the second half of a long plan the balance itself has become the largest source of new growth, which is why 400 a month over 30 years produces well over double the result of the same amount over 20 years.
Does this calculator account for market crashes?: No. It compounds one constant annual rate for the entire period, so it cannot show what happens if a downturn hits early versus late in the plan, even though that timing changes the real outcome for two savers with the same average return. Use the output as a steady-state anchor, not a stress test.
Should I include my employer's 401(k) match in the monthly figure?: Yes, if you want the projection to reflect what actually lands in the account each month. A match is effectively an extra contribution on top of your own, so leaving it out understates the ending value, sometimes substantially, depending on how generous the match is.
How often should I revisit the numbers I entered?: At least once a year, and after any change to income, contribution amount, or the return assumption you are comfortable using. A projection built on a rate or a monthly amount from several years ago will drift away from reality faster than most people expect, particularly after a raise or a change in asset allocation.

Sources

U.S. Securities and Exchange Commission — Investor.gov glossary: Dollar Cost Averaging — Official definition of dollar-cost averaging as investing equal amounts at regular intervals regardless of price (accessed 2026).
IRS — Retirement topics: IRA contribution limits — Annual IRA contribution limits that cap how much monthly investing can be sheltered inside a traditional or Roth IRA (2025 tax year figures).