How your average cost is worked out
Regular investing means the same amount of money goes in period after period, so the number of shares you get changes with the price: a cheap period buys more shares, an expensive period buys fewer. The page works each period out on its own, then averages the lot.
- Shares bought in a period = amount invested that period ÷ price per share that period
- Total invested = amount1 + amount2 + …
- Total shares = shares1 + shares2 + …
- Average cost per share = total invested ÷ total shares
- Market value = total shares × current price
- Profit / loss = market value − total invested
- Return = (profit / loss ÷ total invested) × 100
Average cost per share = (a1 + a2 + … + an) ÷ (a1÷p1 + a2÷p2 + … + an÷pn)
where a is the amount put in that period and p is the price per share paid in that period. The top of that fraction is the money in; the bottom is everything those periods bought. It is the same weighted average used everywhere on this site — the shares are what do the weighting, and they come out of the division above.
Worked example: three periods of 1,000 each, at 50, 60 and 45. The shares are 1,000÷50 = 20.0000, 1,000÷60 = 16.6666 and 1,000÷45 = 22.2222, so 58.8888 shares for 3,000.00 invested, and an average cost of 3,000.00 ÷ 58.8888 = 50.9434. Type those three rows in and the page returns that figure.
Notice it is below the plain average of the three prices (51.6667). The cheap third period bought more shares than the dear second one, so it pulls the average down harder than the second period pulls it up. That is the whole point of the weighting, and it is why a plain average of your prices is the wrong number.
Rounding: every figure on this page is rounded down, never up — the same rule as the rest of the site. Share counts and prices are shown to four decimals and amounts to two, so the number you read is never larger than the one that was computed. Share counts keep all four decimals even when they come out whole, so every period lines up with the total. The total shares is the sum of the per-period figures exactly as they are printed beside each row, so the column and the total agree with each other.
What is counted, and what is not
This page uses only the amounts and the prices per share you type in. Nothing else goes into the arithmetic.
- Not counted: commissions and fees, taxes, dividends, stock splits and other corporate actions, partial sales, and currency conversion. There is no field for any of them.
- No live prices. This page never fetches a quote and has no connection to a market data source, so it can never show you a price that is not real. Every price on the page — each period's, and the current one — is yours to type.
- Not built: several tickers at once, saving your history, signing in, or placing an order. There is no account here and nothing is stored.
- Fractional shares are counted in full. 1,000 at 60 gives 16.6666 shares, not 16. If your broker only handles whole shares, your own figure will differ from this one.
If you want a commission to show up in the average, subtract it from that period's amount before typing it in — the shares come out slightly lower and the average slightly higher. Left as it is, the result is a before-fee figure. Amounts are shown in whatever currency you typed; no exchange rate is applied anywhere.
The result is the average cost of the periods you entered. It is not a view on whether that schedule suits you, and this page takes no position on it.
Frequently asked questions
Is a DCA calculator the same thing as a dollar cost averaging calculator?
Yes — DCA is short for dollar-cost averaging, and both names ask for the same arithmetic: money in per period, price per period, and the average cost that comes out. This is one page, not two.
What does a DCA calculator work out, exactly?
Three things from the figures you type: the shares each period bought, your totals (money in and shares held), and your average cost per share. If you also type a current price, it adds market value, profit or loss and return. That is the whole page.
Do I enter the amount I invested, or the number of shares I bought?
The amount. That is what regular investing fixes in advance — the money — while the number of shares follows from the price. The page divides for you and prints the shares next to each row. If you already know the share counts and want the average of those purchases instead, use the stock average calculator on the home page, which takes shares directly.
Can it look up the price I paid, or the price now?
No. There is no price lookup on this page and no connection to any market data source, by design — a fetched price can be wrong, delayed, or for the wrong ticker, and this page would rather show nothing than show a number it did not get from you. Type the prices yourself.
Does it count fees, commissions or taxes?
No. There is no field for any of them, so the average you get back is before those costs. To see one period with a commission in it, subtract the commission from that period's amount before typing it in; the shares come out lower and the average higher. Taxes on a sale are outside this page entirely — it averages what you bought, not what you owe.
How many periods can I enter?
As many as you need. The page starts with two periods — one period on its own just returns the price you typed — then use + Add period for each extra one and the × on a row to remove it. There is no cap.
How is this different from the other calculator in this site's menu?
The home page takes the share counts you already own and averages them. This page takes the money you put in each period and works the share counts out first, which is the regular-investing way round. The average both pages return is the same weighted average; only the inputs differ. If you are working out what a further purchase would do to an average you already have, use the average down calculator.
Does this page tell me whether I should keep investing on a schedule?
No, and nothing here should be read that way. The page does the arithmetic on the periods you enter; it does not compare approaches, rank them, or tell you what to do with your money. It answers one question only: given these amounts and these prices, what is my average cost per share?
Does it work on my phone, and do I need an account?
Yes to the first, and no to the second. The fields stack to a single column on a narrow screen and the results stay inside the width of the page. There is no sign-up, no pop-up and nothing to install: the whole calculation runs in your browser, and your numbers are not sent anywhere.