Dollar-Cost Averaging Calculator

About the Dollar-Cost Averaging Calculator

Dollar-cost averaging is the practice of investing a fixed dollar amount at regular intervals regardless of price, and its quiet power is that it automatically buys more shares when prices are low and fewer when prices are high. This calculator lets you plug in a price history and see exactly how that mechanic played out: how many shares you accumulated, at what average cost, and what the position is worth.

You set the amount invested each period and enter the price for each period in the table. The tool buys as many shares as your fixed dollar amount allows at each price, then reports total invested, total shares, average cost per share, current value at the latest price, and your gain and return.

The revelation for most people is that the average cost you pay ends up below the simple average of the prices, because your fixed budget scoops up extra shares during the dips. Seeing that gap in real numbers is the best case for automating contributions and ignoring the urge to time the market.

How the Dollar-Cost Averaging Calculator works

In each period the tool divides your fixed contribution by that period's price to get the shares purchased, then adds them to a running total. Total invested is simply your per-period amount multiplied by the number of periods, and total shares is the sum of all the fractional purchases.

Average cost per share is total invested divided by total shares. This is a dollar-weighted (harmonic) average, which is why it lands below the plain arithmetic average of the prices: the periods where price was low bought disproportionately many shares and pull the average down.

Current value is total shares multiplied by the price in the final period, which the tool treats as the present price. Gain is current value minus total invested, and return is that gain divided by total invested. Adding or removing rows renumbers the periods automatically, so you can model any number of contributions.

Worked example

With the defaults, you invest $500 per period across 12 periods with prices ranging from $90 to $130. That is $6,000 invested in total. Because your fixed $500 buys more shares when the price dips to $90 and fewer at $130, you accumulate about 55.32 shares, giving an average cost of $6,000 / 55.32 = $108.47 per share.

The simple arithmetic average of those twelve prices is $109.83, so dollar-cost averaging got you in at $108.47, meaningfully below the naive average, purely from the discipline of a fixed budget. At the final price of $122, your 55.32 shares are worth about $6,749, a gain of $749 for a 12.5% return.

The example captures the whole thesis in one screen: you did not predict a single price, yet you still bought below the average price and finished ahead. That is the structural edge dollar-cost averaging provides in a choppy, upward-drifting market.

Tips & common mistakes

• Keep the contribution amount truly fixed. The strategy's advantage comes from buying a constant dollar amount, which mechanically buys more shares when prices fall; varying the amount based on how you feel about the market defeats the purpose.
• Compare the average cost the tool reports against the simple average of your prices. The gap between them is the concrete benefit dollar-cost averaging delivered over that stretch.
• Remember the current value depends entirely on the last price you enter. In a market that ended on a dip, even a well-averaged position can show a temporary loss, which is normal and not a failure of the method.
• Use realistic prices rather than a steadily rising line. Dollar-cost averaging shines precisely when prices are volatile, so a flat upward ramp will understate its advantage over lump-sum buying.
• The tool ignores commissions and any spare cash left over each period. If your broker charges per-trade fees or you cannot buy fractional shares, your real average cost will be slightly higher than shown.

Dollar-Cost Averaging Calculator: frequently asked questions