Dollar-cost averaging (DCA) explained, with a worked example
Dollar-cost averaging means investing a fixed amount at regular intervals, whatever the price — so you buy more units when prices are low and fewer when high.
What DCA is
Dollar-cost averaging (DCA) is a simple rule: invest the same amount of money at fixed intervals — every week or every month — regardless of what the price is doing. Because the amount is fixed, the number of units you buy changes automatically: more when the price is low, fewer when it is high.
It is how many people already invest without naming it, through monthly contributions to a pension or savings plan. The technique works for any asset you can buy in small amounts: index funds, stocks, gold or crypto.
How the average cost works
Your average cost per unit is the total invested divided by the total units bought:
Average cost = total invested ÷ total units Units bought each time = fixed amount ÷ price that day
With equal amounts, this average is the harmonic mean of the prices you paid, which is never above their simple arithmetic average. That is the mathematical core of DCA: it automatically tilts your purchases towards the cheaper periods.
A worked example
Invest $100 a month for three months at prices of $10, $5 and $10. You buy 10, 20 and 10 units — 40 units for $300, an average cost of $7.50 per unit, although the average price was $8.33. When the price returns to $10, your 40 units are worth $400: a 33% gain even though the price ended exactly where it started. You can test your own scenarios with the DCA calculator.
The same mechanism cuts the other way in a long, steady decline: each purchase is cheaper, but the whole position keeps falling. DCA lowers the average entry price; it doesn't turn a bad investment into a good one.
DCA versus a lump sum — and the costs
If you already have a large sum, investing it all at once has historically beaten spreading it out more often than not, simply because markets have risen more often than they have fallen. A frequently cited Vanguard study found that lump-sum investing came out ahead roughly two-thirds of the time over the periods it examined. DCA's real advantages are behavioural: it removes the pressure to pick the perfect moment and limits the regret of investing everything just before a fall.
Watch the fees: a fixed commission on every small purchase can eat a meaningful share of each contribution. And DCA only works if you keep going through downturns — pausing contributions when prices fall defeats its purpose.
Frequently asked questions
Is dollar-cost averaging a good strategy?
For most people investing from a regular income, yes: it builds discipline, spreads timing risk and is easy to automate. It doesn't guarantee a profit or protect against losses in a falling market.
Is DCA better than investing a lump sum?
Not on average. In rising markets a lump sum has more often produced higher returns, because the money is invested for longer. DCA is a way to reduce timing risk and regret, not to maximise expected return.
How often should I invest with DCA?
Monthly is common because it matches salaries. The exact frequency matters less than consistency and keeping transaction costs low.