Stock Average Cost Calculator
Bought the same stock at different prices? Add each buy lot to find your true average cost per share, how many shares you hold, and — with a current price — whether you're up or down.
Estimates are for illustration and education only — not financial advice. This tool ignores commissions, fees and taxes, which affect your true cost basis.
What your average cost really tells you
Your average cost per share is simply your total money invested divided by your total shares. When you buy the same stock more than once at different prices, this blended number — not any single purchase price — is your real break-even point.
Averaging down, and its risk
Buying more shares as a price falls lowers your average cost, so the stock needs a smaller rebound for you to break even. That's "averaging down." It can work well for a solid company on sale — but it also means putting more money into something that's losing, so it magnifies the damage if the decline is justified.
Cost basis and taxes
For tax purposes your cost basis also includes commissions and fees, and brokers may track it per-lot rather than as a single average. This calculator gives the simple blended average; check your brokerage statements for the exact figures at tax time.
Once you know your position, project where regular investing could take it with our dollar-cost averaging calculator.
The average cost formula
Your average cost per share is a weighted average — bigger purchases pull it toward their price. It's just total money in, divided by total shares held.
Averaging down vs averaging up
Adding shares at a different price always moves your average. Whether that's smart depends entirely on why the price moved.
Averaging down lowers avg
- Buying more as the price falls pulls your average cost down
- Needs a smaller rebound to reach break-even
- Sensible for a strong company temporarily on sale
- Risky if the drop reflects a real, lasting problem
Averaging up raises avg
- Buying more as the price rises lifts your average cost
- Adds to a position that's already working
- Confirms conviction in a winning holding
- Reduces your margin of safety if momentum reverses
Average cost is your break-even. It's the price the stock must reach for your whole position to be in the black — a far more useful reference point than any single purchase price when you own multiple lots.
Cost basis and tax. For taxes, your cost basis also includes commissions and fees, and brokers may report it per-lot (allowing methods like FIFO or specific-lot identification) rather than as one blended average. This tool gives the simple average; rely on your brokerage's cost-basis records at tax time.
How each lot shifts the average
Watch the running average move as lots are added. A larger lot at a lower price does the most to pull the average down.
| Lot | Shares | Price | Cost | Running avg |
|---|---|---|---|---|
| Buy 1 | 10 | $120 | $1,200 | $120.00 |
| Buy 2 | 15 | $95 | $1,425 | $105.00 |
| Buy 3 | 8 | $140 | $1,120 | $113.48 |
The big middle lot at $95 dragged the average from $120 down to $105; the smaller, pricier third lot nudged it back up only modestly. Weight — shares times price — is what matters, not the number of transactions.