Stock Average Calculator

When you buy the same stock more than once at different prices, a stock average calculator tells you what you actually paid per share on average. It multiplies the shares in each purchase by the price you paid, adds those totals together, and divides by the total number of shares. That weighted result is your true average cost per share, the number that sets your break-even point.

This is not a profit tool. It never asks for a sell price and it cannot tell you what you made. It answers the earlier question of what your shares cost you across all your purchases, before you sell anything. Every calculation runs in your browser, and nothing you type is sent or saved anywhere.

1. Enter the number of shares and the price per share for your first purchase. Add a commission in the optional field if your broker charged one.
2. Press "Add purchase" for each additional buy, up to 10 lots. Leave a row blank if you do not need it. Blank rows are ignored.
3. Optionally type the current market price per share to see your unrealized gain or loss against your average.
4. Press Calculate. The average cost per share appears first and large, then the total shares, total cost, break-even price and the step-by-step math.
5. Press Reset to clear the form and start over.

Average cost per share = Total cost ÷ Total shares. Total cost is the sum of (shares × price per share + commission) across every purchase. Total shares is the sum of the shares in every purchase.

P is the price per share in one purchase, Q is the number of shares in that purchase, and each purchase counts separately. A commission is added to the cost of the purchase that paid it, so the average reflects the money you truly spent.

Why It Must Be a Weighted Average

A simple average treats each purchase as equal, but your money is not spread equally. If you buy 100 shares at $50 and 200 shares at $40, two-thirds of your money went in at the lower price. The weighted average gives each purchase influence in proportion to its size, which is why the answer is $43.33 instead of the $45 midpoint. A calculator that averaged only the prices would mislead you whenever the lots are uneven.

You buy 100 shares at $50, then later buy 200 shares at $40. Here is the full math.

Cost of the first buy: 100 × $50.00 = $5,000.00. Cost of the second buy: 200 × $40.00 = $8,000.00. Total cost: $5,000.00 + $8,000.00 = $13,000.00. Total shares: 100 + 200 = 300. Average cost per share: $13,000.00 ÷ 300 = $43.33.

The simple average of the two prices is ($50 + $40) ÷ 2 = $45, and that is wrong. It ignores the fact that twice as many shares were bought at $40. Try it above with 100 shares at 50 and 200 shares at 40 to see the same result with every step shown.

Averaging down means buying more shares below your current average, which pulls the average down. Averaging up means buying more shares above your current average, which pushes it up. Both change the average and the break-even price, and both change how much money you have at risk.

Averaging Down

You hold 100 shares bought at $180, an $18,000 position. The price falls to $162 and you buy 50 more shares for $8,100. Your new total is $26,100 across 150 shares, so the average drops to $174.00. You now break even $6 lower, but you have $8,100 more exposed to a stock that is falling.

Averaging Up

You hold 200 shares bought at $45, a $9,000 position. The price rises to $52.50 and you add 100 shares for $5,250. Your new total is $14,250 across 300 shares, so the average rises to $47.50. You break even higher, but every extra dollar is riding a stock that is already rising.

Buying on a fixed schedule, for example every month, uses the same weighted-average math. Each purchase is one more lot in the formula, and the average blends them all by size. To project how regular contributions might grow over time with compounding, try the investment calculator.

Averaging down feels good because the average falls, but the average is not the whole story. Every new purchase adds money to a losing position, so the total amount at risk grows with each buy. The example above raised the exposure from $18,000 to $26,100 for a $6 improvement in the average.

The classic danger is throwing good money after bad. If the stock keeps falling because the business itself is weakening, each new purchase lowers the average a little while the position loses a lot. Averaging down into a broken company can turn a small loss into a large one.

Set the rules before you buy more. Decide the maximum share of your portfolio that one stock may take, decide how many times you are willing to add, and only average down while the reason you bought the stock still holds. Position sizing is the guardrail that keeps a cheaper average from becoming a bigger loss.

The basic result covers share prices and the commissions you enter. It does not include taxes, which depend on your country and how long you held the shares. It does not subtract dividends you received, so your true return is slightly better than the break-even suggests. Track dividend income separately with a dividend calculator to see the full picture.

To fold a brokerage fee into your cost basis, add it to the commission field of the purchase that paid it. A $10 fee on the $5,000 first buy makes that lot $5,010, and with a $10 fee on each of the two example lots the average moves from $43.33 to $43.40.

Stock splits also change the per-share number without changing your money. After a 2-for-1 split, the 300-share example becomes 600 shares and the average halves from $43.33 to about $21.67. The total cost is still $13,000, just spread over twice as many shares.

The stock average calculator answers what you paid. It takes your purchases and returns your average cost per share, with no sell price involved. Use it while you still hold the stock, when you want your break-even point or a clean cost basis for your records.

The Stock Profit Calculator answers what you made. It takes a buy price and a sell price and turns them into a dollar gain or loss. Once you know your average cost and eventually sell, the Stock Profit Calculator turns your buy and sell prices into an exact gain or loss.

In short, average first and profit later. One tool prices the position, the other scores the trade.

This calculator gives an estimate for planning and is for informational purposes only, not investment advice. Actual results depend on your broker, fees and taxes. See our disclaimer.