Online Tool Store
DCA Calculator
Project the value of regular fixed investments at an assumed return, or paste your buy prices to find your true average cost per unit. Runs in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
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This is arithmetic, not financial advice, and it does not fetch any live prices. Real returns are not a steady percentage — they arrive in an order that matters, and the projection ignores fees, taxes, dividends and inflation. Use it to compare scenarios, not to predict one.
How to use it
- Enter how much you invest each time, and how often.
- To look ahead, set the years and an assumed annual return.
- To look back, switch to Work out my average cost and paste the price at each buy.
- Read the year-by-year or buy-by-buy table underneath the summary.
The projection, in full
Level contributions compounding at a fixed rate is an annuity, and it has a closed form:
value = amount × ((1 + r)^n − 1) / r where r = annual rate / buys per year
and n = years × buys per year
With 500 a month at 7% for 20 years that is 120,000 contributed and about 260,463 at the end — so more than half the final figure is growth rather than money you put in. The 7% is treated as a nominal rate compounded once per buy, which works out to an effective 7.23% a year; that is the usual convention, but it is worth knowing the tool is not quietly using a different one.
The year-by-year table is built by stepping through every period one at a time rather than by reusing the formula, so the two are independent calculations that have to agree. They do, including at a 0% rate, where the closed form would otherwise divide by zero.
Why your average cost is not the average price
This is the part most DCA calculators skip. Spend a fixed amount at each of these six prices and the result is not the price average:
prices 100, 80, 125, 90, 110, 100
average price 100.83 (the arithmetic mean)
your cost/unit 98.84 (the harmonic mean)
Fixed money into a varying price gives the harmonic mean, and the harmonic mean is below the arithmetic mean for any set of prices that are not all identical. That inequality is the entire mechanism of averaging in — not a market opinion, just what dividing by different numbers does.
It is also why the comparison row matters. On that same series the six buys end up worth slightly more than the same money invested at the first price, because the price dipped in the middle. Change the series so it rises steadily and the lump sum wins instead. Averaging in is a way of not betting everything on one day; it is not a way of getting a higher return.
FAQ
What is dollar-cost averaging?
Putting the same amount of money in at regular intervals instead of all at once. Because the amount is fixed and the price is not, you automatically buy more units when the price is low and fewer when it is high.
Why is my average cost lower than the average price?
Because a fixed amount of money buys more units at low prices, so the cheap buys carry more weight. Mathematically your average cost is the harmonic mean of the prices, which is always below the plain average unless every price is identical. In the worked example the gap is about 1.99 per unit.
Does averaging in beat investing the lump sum?
Not reliably, and this tool will not claim it does. Averaging in wins when the price falls after you start and loses when it rises, and since markets rise more often than they fall, a lump sum comes out ahead more often historically. What averaging in reliably reduces is the consequence of picking a bad single day — which is a risk argument, not a returns argument.
Which return figure should I put in?
Whatever you can defend, and then try a lower one. Nobody knows the future rate, so the honest use of the projection is comparison — see what changes between 5% and 8%, or between 20 and 25 years, rather than treating any single output as a forecast.
Does the "buy at start or end of period" setting matter?
A little, and always in the same direction: buying at the start gives every contribution one extra period of growth. On the default figures it is the difference between about 260,463 and 261,983 — roughly 1,500 over twenty years, or 0.6%.
Does it fetch live prices for a stock or coin?
No. There is no price feed and no account connection — every number comes from what you type. For the average-cost mode you paste your own buy prices, which also means the tool works for anything you can put a price on.
How we compare
| Feature | Online Tool Store | Typical DCA calculators | Broker or portfolio app |
|---|---|---|---|
| Projection and average cost in one tool | ✓ | Usually one or the other | Average cost only |
| Shows average cost against average price | ✓ | ✗ | ✗ |
| States the compounding convention it uses | ✓ | ✗ | Not applicable |
| No account, no email, nothing uploaded | ✓ | Often gated | ✗ |
| Works for any asset you can price | ✓ | Often one asset class | Only what you hold there |
| Pulls live prices and your real holdings | ✗ | Sometimes | ✓ |
| Fees, dividends, tax and inflation | ✗ | ✗ | ✓ |
Good for the two questions people actually ask — what might this become, and what did I pay per unit — with the arithmetic stated openly. It has no price feed and knows nothing about your fees, dividends or tax, so for tracking a real portfolio your broker's own figures are the ones to trust.