Stock Average Calculator

How to use the calculator

1. Choose a mode. Average shows the position you hold; Target solves for the shares to buy.
2. Enter your purchases. For each buy, type the number of shares and the price per share. Fractional shares are fine. Open the extra rows for up to ten purchases; empty rows are ignored.
3. Add fees if you paid any. A commission or other trading fee goes in the fee field of that purchase, in dollars.
4. Current price (optional). Enter today's price to see market value and your unrealized gain or loss in dollars and percent.
5. Target mode: enter the price you expect to pay, the average you want to reach and an optional fee.

How the average cost is calculated

The calculator adds up what every purchase cost and divides by the total number of shares:

Average cost = (Σ shares × price + Σ fees) ÷ Σ shares

That is your cost per share including fees, which matches how the IRS describes basis for stock you buy: the purchase price plus costs such as commissions. A second figure, average price, leaves fees out so you can compare it with the number your broker shows.

Gain or loss = shares × current price − total cost. The percentage is measured against total cost, fees included.

Target mode

To reach a target average T by buying x shares at price P with fee f:

x = (total cost + f − T × shares held) ÷ (T − P)

Because you may only be able to buy whole shares, the calculator also rounds x up and shows the average you actually end with. A target is reachable only if it lies between the new price and your current average: you can't average down to $40 by buying at $45.

Worked examples

1. Three purchases of the same stock

You bought 100 shares at $48.50, 50 at $42.00 and 75 at $39.20. That is 225 shares for $9,890.00, an average cost of $43.96 per share (the calculator shows $43.9556). The first purchase is 44.4% of the position. At a current price of $41.00 the shares are worth $9,225.00, an unrealized loss of $665.00, or −6.72%.

If each trade had a $4.95 commission, fees total $14.85, the average cost rises to $44.02 while the average price stays at $43.96, and the loss becomes $679.85 (−6.86%).

2. Averaging down

Each step closer to the new price costs much more. Getting to $40 takes $16,910.00, well over the $9,890.00 you have already invested.

3. Averaging up

If the stock instead trades at $52.00 and you accept a $45.00 average, the exact answer is 33.57 shares. Rounded up to 34 shares, the purchase costs $1,768.00 and leaves you with 259 shares at an average of $45.01.

How to read the result

Your average cost is your break-even price before selling costs. It says nothing about where the price goes next. Averaging down lowers your break-even, but it also puts more money into a position that has already fallen. This page is a calculation, not a strategy recommendation.

Not modeled: sales, lot-by-lot identification, wash-sale adjustments, reinvested dividends and stock splits. After a split, enter split-adjusted figures: in a 2-for-1 split the example above becomes 200, 100 and 150 shares at $24.25, $21.00 and $19.60, still $9,890.00 in total, with an average of $21.98.