Stock Average Calculator

The Stock Average Calculator combines completed purchase lots into one weighted average cost per share. Enter shares and price for each lot, then optionally add the same brokerage fee for every valid lot and a current market price.

Method

For each lot, the calculator multiplies shares x price to get purchase amount. It then adds the brokerage fee once per lot and divides total cost by total shares: $\\text{Average price}=\\frac{\\sum(\\text{shares}\\times\\text{price})+(\\text{fee}\\times\\text{valid lots})}{\\sum\\text{shares}}$ Only rows with both shares and price greater than zero are included. With a current price, it also reports current value, unrealised profit or loss, and percentage return against total cost.

Worked example

Suppose you buy 10 shares at $100 and 20 shares at$80, with a $5 fee per trade. Purchase cost is `$1,000 + $1,600 =$2,600; fees add $10`, so total cost is `$2,610. The weighted average is $2,610 / 30 =$87.00per share. If the current price is $90, current value is$2,700` and unrealised profit is `$90` (about 3.45%).

Interpret the result

Average price is a break-even reference before taxes and future trading costs. It is not the average of the quoted prices unless each lot has the same share count. A lower-priced purchase affects the result in proportion to its shares.

Limitations

The calculator models purchases only. It does not track sales, dividends, stock splits, wash-sale adjustments, tax-lot selection, foreign exchange, or broker-specific cost-basis rules. Brokerage fee is assumed identical for every included lot.

Questions

Why is my result different from averaging the prices?

Because the tool uses a weighted average: a larger lot has more influence.

Does current price change average cost?

No. It only adds current value and unrealised return.

Can I include fractional shares?

Yes. Share and price inputs accept decimal values.