What Is Dollar-Cost Averaging?
Dollar-cost averaging means investing a fixed amount on a fixed schedule — $500 on the first of every month, say — no matter what the price happens to be. Because a fixed sum buys more shares when prices are low and fewer when they are high, your average cost lands below the average price. In the worked example below, six $500 investments produced an average cost of $40.91 per share while the prices themselves averaged $44.17. It is arithmetic, not market timing.
The short answer
Dollar-cost averaging is investing the same amount of money at regular intervals, regardless of price. You decide the amount and the schedule once — $500 a month, every month — and then stop making decisions.
The effect is automatic: the fixed sum buys more units when prices are low and fewer when prices are high, so your purchases are naturally weighted toward the cheaper months. That pulls your average cost per share below the average price over the same period.
Model it yourself: the investment growth calculator and the future value calculator both project regular monthly contributions over time.
How it works
There are only three moving parts:
- A fixed amount. The same dollar figure each time, not a fixed number of shares.
- A fixed schedule. Usually monthly, because that is how most people are paid.
- No price judgement. You buy whether the market is up, down or flat — that is the whole discipline.
The key detail is the first one. Buying a fixed number of shares each month would spend more when prices are high, which is the opposite of what you want. Fixing the dollar amount is what does the work.
A worked example
Suppose you invest $500 on the first of each month for six months, and the price moves around a lot:
| Month | Price per share | $500 buys |
|---|---|---|
| 1 | $50 | 10.00 shares |
| 2 | $40 | 12.50 shares |
| 3 | $25 | 20.00 shares |
| 4 | $40 | 12.50 shares |
| 5 | $50 | 10.00 shares |
| 6 | $60 | 8.33 shares |
You invested $3,000 in total and ended up with 73.33 shares. That works out to an average cost of $40.91 a share — noticeably below the simple average price of $44.17. Look at month 3: the same $500 bought twice as many shares as month 1, purely because the price was low.
At the month-6 price of $60, those shares are worth $4,400 — a $1,400 gain on $3,000 invested.
Versus a lump sum
The fair comparison is the same total invested, committed all at once at the start. With $3,000 at the month-1 price of $50 you would have bought 60 shares:
| Approach | Shares acquired | Value at $60 | Gain |
|---|---|---|---|
| Dollar-cost averaging | 73.33 | $4,400 | $1,400 |
| Lump sum at $50 | 60.00 | $3,600 | $600 |
Dollar-cost averaging came out $800 ahead — but only because the price dipped after month 1 and recovered. Change that assumption and the answer flips. If the price had risen steadily from $50 to $75 instead, the same six $500 investments would be worth about $3,669, while the lump sum would be worth $4,500 — the lump sum wins by roughly $831, because all the money was invested from day one.
That is the honest summary: dollar-cost averaging wins when prices fall and then recover; a lump sum wins when prices mostly rise. Since markets rise more often than they fall, lump-sum investing wins more often on average — which is exactly why most people use dollar-cost averaging for a different reason.
Why the average cost is always lower
The result in the example is not a coincidence of the numbers chosen. When you invest a fixed dollar amount, your average cost per share is the harmonic mean of the prices you paid, while the “average price” people quote is the ordinary arithmetic mean:
The harmonic mean is always less than or equal to the arithmetic mean, and they are equal only when every price is identical. In the example, the harmonic mean of $50, $40, $25, $40, $50 and $60 is exactly $40.91 — matching the average cost — against an arithmetic mean of $44.17.
So the cost advantage over the average price is guaranteed by the arithmetic whenever prices vary. What is not guaranteed is beating a lump sum, which depends entirely on which direction prices moved. It is the same distinction between averaging methods covered in CAGR vs average annual return.
When it makes sense
- When you are investing from income. Most people never face the lump-sum question — money arrives monthly, so investing monthly is simply how a portfolio gets built.
- When you want to remove timing decisions. A fixed automatic transfer means you never have to judge whether today is a good day to buy.
- When a falling market would otherwise scare you off. Steady buying reframes a dip as cheaper shares, which makes it easier to keep going.
- Less so when you already hold a large cash sum and a long horizon — historically, investing it sooner has won more often, though spreading it out reduces the risk of one badly timed entry.
Whatever the schedule, consistency is what compounds — see how much you should invest every month.
Assumptions
- Illustrative prices. The six-month sequence is chosen to show the effect clearly, not to represent any real investment.
- Fractional shares allowed, and purchases made on the same day each month.
- No fees, commissions or taxes. Per-trade costs would weigh more heavily on frequent small purchases.
- No dividends or reinvestment, which would raise both approaches.
Frequently asked questions
The bottom line
Dollar-cost averaging is investing a fixed amount on a fixed schedule and letting the arithmetic work: a fixed sum buys more shares when prices are low, so your average cost lands below the average price — $40.91 against $44.17 in the example above. It beats a lump sum when prices dip and recover, and loses to one when prices climb steadily. Its real value for most people is not outperformance but consistency: it turns investing into a habit that survives bad months.
Project your own monthly contributions with the investment growth calculator, or read how compound interest works.
Disclaimer: This page is for general educational purposes only and is not financial advice. The price sequences are illustrative, not predictions; dollar-cost averaging does not guarantee a profit or protect against loss in a declining market. Consider speaking with a qualified financial professional before making decisions about your own money.