How it works
You choose an amount and a schedule, then stick to it. Because the amount is fixed, you buy more units when prices are low and fewer units when prices are high. Over time, this smooths out the price you pay.
A worked example
Suppose you invest $500 a month into the same ETF for six months, and the price moves around. For simplicity, this example ignores brokerage.
| Month | Amount | Price per unit | Units bought |
|---|---|---|---|
| 1 | $500 | $50.00 | 10.00 |
| 2 | $500 | $40.00 | 12.50 |
| 3 | $500 | $31.25 | 16.00 |
| 4 | $500 | $40.00 | 12.50 |
| 5 | $500 | $50.00 | 10.00 |
| 6 | $500 | $62.50 | 8.00 |
| Total | $3,000 | 69.00 |
You invested $3,000 and own 69 units. Your average cost per unit is $3,000 ÷ 69 = about $43.48.
The simple average of the six prices is ($50 + $40 + $31.25 + $40 + $50 + $62.50) ÷ 6 = about $45.63. Your average cost is lower than the average price because the fixed amount bought more units in the cheaper months.
At the final price of $62.50, the 69 units are worth about $4,313 — an unrealised gain of roughly $1,313. But had the price ended at $35, the same units would be worth about $2,415, a loss of around $585. DCA changed the average cost; it did not decide the outcome.
Investing through different market conditions
In a falling market, DCA keeps buying at lower prices, which some investors find reassuring and others find hard to continue. In a rising market, each purchase costs more, so you accumulate fewer units over time. In a sideways, choppy market, DCA's smoothing effect is most visible. None of these outcomes is guaranteed; it depends entirely on the path prices take.
Volatility
DCA does not reduce the volatility of what you own. A volatile asset bought gradually is still volatile. What it reduces is the risk that all your money goes in at one particularly bad moment.
DCA versus lump-sum investing
If you already have a large sum available, you face a choice: invest it all now, or spread it out. Historically, markets have risen more often than they have fallen over long periods, so investing a lump sum immediately has often — though not always — ended up ahead, simply because the money spent more time invested.
Spreading it out, on the other hand, reduces the chance of investing everything just before a fall, and many people find it easier emotionally. It is a trade-off between expected outcome and peace of mind, and the right balance is personal.
For most people, though, the choice does not arise: they invest from income as it is earned. In that case regular investing is not so much a strategy as the natural way their money reaches the market.
Advantages
- Builds a consistent habit and removes the need to judge when to buy.
- Matches regular income.
- Reduces the impact of buying everything at a single high point.
- Can make market falls feel less stressful, as later purchases come at lower prices.
Disadvantages
- Money waiting to be invested may sit in cash during a rising market.
- More transactions can mean more brokerage.
- It can create a false sense of safety about a risky asset.
- It still requires the discipline to continue when prices are falling.
Fees and transaction costs
Frequent small purchases can be expensive if each one carries a fixed fee. A $10 brokerage fee on a $200 purchase is 5% of the investment before the price has moved at all. On a $2,000 purchase it is 0.5%. Some investors adjust the frequency — monthly instead of weekly, for example — so fees take a smaller share. Always include fees in your cost basis, as explained in Understanding Cost Basis.
Common misconceptions
- "DCA guarantees a profit." It does not. If the asset falls and stays down, a DCA investor loses money.
- "DCA protects against losses." It spreads the timing of purchases; it does not protect the value of what you own.
- "DCA always beats lump-sum." Historically it often has not, when a lump sum was available.
- "DCA works for any investment." Regularly buying something that declines permanently just means buying more of it.
- "Your average cost is the average of the prices." With fixed amounts, your average cost is usually lower than the simple average price, as the example shows.
Observing DCA in Compndr
Compndr does not tell you what to buy, how much to invest or when. What it can do is show you the effect of the habit you choose. Each purchase you record or import updates the holding's cost basis and average cost, so you can watch how it changes. The Performance History chart and Journey show how contributions and your portfolio value develop over time, and the Projection tool lets you model regular contributions using assumptions you set yourself — as a mathematical model, not a prediction.
To understand why a rising portfolio value is not the same as a good return when you contribute regularly, read Understanding Your Portfolio Performance.