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Dollar-Cost Averaging Calculator

Enter your per-period amount, periods and prices to see your DCA value and ROI.

How it is calculated

The tool takes four inputs: the amount invested each period, the number of periods, the average price you paid per share, and today's share price. Total invested is amount × periods. Shares owned are total invested / average price, and current value is shares × current price. Return on investment is (value − invested) / invested × 100. The average price is something you enter, not something the tool derives from a price history, so work it out first (total spent divided by total shares bought). Fees, dividends, taxes and the timing of each contribution are not included, and the ROI is total return, not annualised. All inputs must be above zero.

Worked example

You invest $200 a month for 24 months at an average cost of $48 per share, and the price is now $55. Total invested: 200 × 24 = $4,800.00. Shares owned: 4,800 / 48 = 100. Current value: 100 × 55 = $5,500.00. ROI: (5,500 − 4,800) / 4,800 × 100 = 14.58%. This is the gain over the whole two years, not per year.

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Common mistakes

  • Entering the price at the first purchase as the average price. With a rising or falling price, your true average over all purchases is different, and the answer shifts with it.
  • Using the simple mean of prices as the average. When the amount is fixed, you buy more shares at low prices, so the average cost is lower than the simple mean (a harmonic mean).
  • Reading the ROI as an annual return. A 14.58% gain over 24 months is not 14.58% a year.
  • Entering the total invested as the per-period amount. The amount field is for a single contribution; the tool multiplies it by the periods.
  • Ignoring fees and taxes, which the calculation leaves out and which lower the real result.

Sources

About this calculator

Dollar-cost averaging (DCA) means investing a fixed amount at regular intervals — weekly, monthly, or per paycheck — instead of committing a lump sum all at once. Because the fixed amount buys more shares when prices are low and fewer when prices are high, it naturally lowers your average cost basis compared to buying a constant number of shares each time, and it removes the pressure of trying to time the market.

This calculator estimates your plan's current value from your per-period contribution, the number of periods, the average price you paid per share, and today's price, then derives your total invested amount and return on investment. It is the strategy behind automatic 401(k) and index-fund contributions, and is widely recommended by advocates of passive, low-effort investing such as the Bogleheads community.

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Comments (1)

  • Editorial team

    The tool needs your average purchase price, and the simple average of prices is not the right one when you invest the same amount each time. Buying 500 at a price of 40 and 500 at a price of 60 gets you 12.5 and about 8.33 shares, an average cost of 48, not 50. Compute total spent divided by total shares first. Did your average come out nearer 48 or 50?

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