How to Calculate Your Weighted Average Share Price
The weighted average share price tells you the true blended cost of your entire stock position. Unlike a simple average, it accounts for how many shares you bought at each price, giving an accurate cost basis for tax reporting and performance tracking in 2026.
The formula is straightforward:
Weighted Avg Price = Total Cost Basis / Total Shares
Where:
Total Cost Basis = (Shares_1 x Price_1) + (Shares_2 x Price_2) + ...
Total Shares = Shares_1 + Shares_2 + ...
For example, buying 100 shares at $50.00 and 50 shares at $60.00 gives a total cost of $8,000.00 across 150 shares, resulting in a weighted average of $53.3333 per share.
Worked Example: Two-Lot Purchase
Consider an investor who makes two purchases of the same stock:
| Detail | Transaction 1 | Transaction 2 | Combined |
|---|---|---|---|
| Shares | 100 | 50 | 150 |
| Price per Share | $50.00 | $60.00 | $53.33 (weighted) |
| Cost | $5,000.00 | $3,000.00 | $8,000.00 |
| % of Total Cost | 62.5% | 37.5% | 100% |
The weighted average ($53.33) sits closer to $50.00 than $60.00 because the larger lot was purchased at the lower price. This is why the weighted method is more accurate than a simple average of $55.00 for determining your true cost basis.
Cost Basis Methods Compared
The weighted average method is one of several IRS-approved approaches for calculating your cost basis. Each method can produce different taxable gains:
- Weighted Average: Blends all purchases into one cost per share. Simplest for ongoing DCA (dollar-cost averaging) investors and the default for many mutual fund accounts.
- FIFO (First-In, First-Out): Assumes the oldest shares are sold first. In a rising market, this typically produces higher capital gains because your cheapest shares are sold first.
- Specific Identification: Lets you choose which exact lot to sell. Useful for tax optimization -- you can sell your highest-cost lot to minimize gains or your lowest-cost lot to realize gains in a low-income year.
Choosing the right method depends on your tax bracket, holding period, and investment strategy. The weighted average method works well for investors who make frequent, similarly-sized purchases over time.
Averaging Down and Position Management
Averaging down is a strategy where you buy more shares after a price decline to lower your overall cost basis. If you hold 200 shares at $100.00 and the stock drops to $80.00, buying another 200 shares brings your weighted average down to $90.00 -- making breakeven $10.00 per share easier to reach.
However, averaging down increases your total exposure. Your total cost rises from $20,000.00 to $36,000.00, and you now hold 400 shares of a declining stock. Only average down when your investment thesis remains intact and you can afford the additional risk.