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Stock Average Calculator
Use this free stock average calculator to work out your true cost per share across several buys. Enter each lot's shares and price, add the current market price, and it gives your average cost, total invested, current value, gain or loss, and the breakeven price your stock needs to reach.
Leave optional lots blank to ignore them. Fees are added to your total invested, which raises your breakeven price slightly.
| Total shares owned | 200 |
| Total invested | $8,000.00 |
| Average cost per share | $40.00 |
| Current value | $8,400.00 |
| Gain / loss | +$400.00 (+5.00%) |
| Breakeven price | $40.00 |
Your lots, averaged
The diagram uses the default example: three lots totalling 200 shares and $8,000 invested, giving an average cost of $40.00 per share.
Value vs price
Position value as the share price moves from $0 to twice your average cost. The line crosses your invested amount at the breakeven price.
How it works
Most investors do not buy all their shares at once. They buy a few shares, then more a month later at a different price, then more again. Each purchase is called a lot, and each lot has its own price. Your average cost per share blends all of them into one number: add up everything you paid across all lots, then divide by the total number of shares. That single number tells you what your position really cost you, and it is the price the stock must reach before you break even.
The math is a weighted average, not a simple average of the prices. A lot of 100 shares at $40 counts twice as much as a lot of 50 shares at $35, because twice as much money went into it. So the calculator multiplies shares by price for each lot, adds those amounts together, and divides by the total shares. With the default example — 100 shares at $40, 50 at $35, and 50 at $45 — the total paid is $4,000 + $1,750 + $2,250 = $8,000 for 200 shares, giving an average cost of $40.00. A plain average of $40, $35, and $45 would give the same $40.00 here by coincidence, but with uneven lot sizes the two methods disagree, and only the weighted version is correct.
Once the average cost is known, the rest follows. Current value is total shares times the current market price. Gain or loss is current value minus total invested, shown both in dollars and as a percentage of the amount invested. The breakeven price is the average cost itself — sell above it and you profit, sell below it and you lose. If you paid brokerage commissions or fees, enter them in the fees field: they are added to the total invested, which nudges the average cost and the breakeven price up a little, giving you the honest figure instead of the rounded one.
Averaging down is the strategy this calculator is most often used for. When a stock falls, buying more at the lower price pulls your average cost down and lowers the price the stock needs to reach for you to break even. That sounds attractive, and sometimes it is — but it also means putting more money into a stock that is already falling. Before averaging down, ask whether the company's prospects have actually changed or only its price. A lower average cost does not fix a bad investment; it just makes a smaller recovery enough to get your money back.
Gain or loss = (Current price − Average cost) × Total shares
The chart shows how your position value changes as the share price moves, from $0 up to twice your average cost. The line crosses the total-invested level exactly at the breakeven price, so you can see at a glance how far the stock needs to move in either direction.
Worked example
Suppose you bought a stock in three lots: 100 shares at $40, 50 shares at $35, and 50 shares at $45. The stock now trades at $42. Enter those numbers and the calculator works like this.
Step 1: Cost of each lot. Lot 1: 100 × $40 = $4,000. Lot 2: 50 × $35 = $1,750. Lot 3: 50 × $45 = $2,250.
Step 2: Total invested is $4,000 + $1,750 + $2,250 = $8,000, and total shares are 100 + 50 + 50 = 200.
Step 3: Average cost is $8,000 ÷ 200 = $40.00 per share. That is also the breakeven price.
Step 4: Current value is 200 × $42 = $8,400. Gain is $8,400 − $8,000 = $400, which is +5.00%.
The tool shows the same result: an average cost of $40.00 per share and a gain of $400.00 (+5.00%). If the price fell to $38 instead, the value would be $7,600 and the loss would be $400 — the same $2 per share move in the other direction.
FAQ
What is the average cost per share of a stock?
The average cost per share is the total amount you paid for all your shares divided by the total number of shares. If you bought 100 shares at $40 and 50 shares at $35, you paid $5,750 for 150 shares, so your average cost is $38.33 per share. It is the price your position needs to reach before you start making a profit.
What does averaging down a stock mean?
Averaging down means buying more shares of a stock you already own after its price has fallen, which lowers your average cost per share. For example, buying 100 shares at $40 and then 100 more at $20 brings your average cost down to $30. It lowers your breakeven price, but it also puts more money into a falling stock, so it only helps if the company recovers.
How do I calculate the breakeven price of my shares?
Your breakeven price is your average cost per share — total invested divided by total shares. Sell above that price and you make a profit; sell below it and you take a loss. Brokerage commissions and fees push the true breakeven slightly higher, so add any fees you paid to the total invested for a more exact figure.
Does the average cost change when I sell some shares?
The average cost of the shares you still own does not change when you sell, because the remaining shares still carry the same blended cost. What changes is your total invested and your total share count. For tax purposes, though, the method your broker uses — average cost, FIFO, or specific lots — decides which shares count as sold and what gain you report.
What is the difference between average cost and current market price?
Average cost is what you paid per share on average; the current market price is what the stock trades for today. The gap between them is your gain or loss per share. If your average cost is $40 and the stock trades at $42, you are up $2 per share. The calculator shows both numbers side by side so the comparison is clear.