Stock Average Calculator
Calculate your blended average cost per share when you've bought stock at multiple prices. Enter each purchase lot — shares and price — to see your true cost basis across all positions.
Enter your purchase lots above — shares and price per share — then click Calculate to see your blended average cost per share.
For educational purposes only. Not financial advice. Read full disclaimer
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Average Cost Formula
Total Cost = Σ(Shares_i × Price_i)
Total Shares = Σ Shares_i
Average Cost = Total Cost / Total Shares
This is a share-weighted average — larger lots have more influence on the result than smaller ones.
Worked Examples
Example 1: Averaging down on a pullback
You bought 50 shares at $150 initially, then added 100 shares at $120 during a pullback.
- Lot 1 cost = 50 × $150 = $7,500
- Lot 2 cost = 100 × $120 = $12,000
- Total cost = $19,500. Total shares = 150
- Average cost = $19,500 / 150 = $130.00 per share
- The pullback purchase moved your breakeven from $150 down to $130 — a $20 improvement per share.
Example 2: Three-lot position in a tech stock
You built a position over three buys: 25 shares at $200, 75 shares at $185, and 50 shares at $195.
- Lot 1 = $5,000. Lot 2 = $13,875. Lot 3 = $9,750
- Total cost = $28,625. Total shares = 150
- Average cost = $28,625 / 150 = $190.83 per share
- The large middle lot at $185 pulled your average below the $200 initial entry — size matters when averaging.
How to Use This Calculator
- Enter shares and price for your first lot — the number of shares purchased and the price paid per share.
- Add additional lots — click the "Add lot" button for each subsequent purchase at a different price.
- Remove lots if needed — click the × button on any row to delete it (minimum 2 rows maintained).
- Click Calculate — see your blended average cost per share, total cost basis, and a plain-English summary.
- Use the result — compare your average cost to the current price to assess whether you're in profit or still underwater across your full position.
Frequently Asked Questions
- What is average cost per share?
- Average cost per share is the total amount you paid for all your shares divided by the total number of shares held. It's your effective breakeven price — the stock must trade above this level for your position to be in profit.
- Why does lot size matter so much?
- This is a weighted average. A lot of 100 shares at $50 has 10 times the influence on your average cost as a lot of 10 shares at $100. Traders use this intentionally — buying larger lots at lower prices to aggressively bring down their average cost basis.
- How is this different from FIFO or LIFO accounting?
- FIFO (first in, first out) and LIFO (last in, first out) determine which specific shares are sold for tax purposes. Average cost is a different method — it calculates one blended price across all shares held. Many brokers offer average cost as a cost basis accounting method.
- Does this work for ETFs, crypto, or options?
- Yes for ETFs and crypto — any asset where you buy units at a price. For options, the math works but "shares" would be contracts and "price per share" would be the premium paid per contract (times 100 for equity options).
- Should I keep averaging down if a stock keeps falling?
- Averaging down (buying more as a stock falls) lowers your average cost but also increases your total exposure and risk. Only average down if your thesis is intact and you have the capital and risk tolerance for a larger position. Never average down to "fix" a bad trade — it can turn a manageable loss into a catastrophic one.