Financial Calculators
Stock Cost-Basis / Averaging Calculator
Calculate your average cost basis across multiple stock purchases. Enter each buy and see total shares, average price, and unrealized gain/loss.
Total Shares: 10
Total Invested: $1,000.00
Avg Cost Basis: $100.00
Current Value: $1,200.00
Gain / Loss: $200.00 (20.00%)
What is averaging down?
Averaging down means buying additional shares of a stock you already own after the price has fallen, with the intention of lowering your average cost per share. If the stock eventually recovers to a price above your new average, you profit (or break even) sooner than you would have based on your original purchase price.
Worked example
| Purchase | Shares | Price | Cost |
|---|---|---|---|
| Initial buy | 10 | $50.00 | $500.00 |
| Averaging down | 20 | $30.00 | $600.00 |
| Total | 30 | $1,100.00 |
Average cost per share = $1,100 ÷ 30 = $36.67. The stock only needs to recover to $36.67 to break even, rather than to the original $50.00.
Averaging down vs. dollar-cost averaging
Averaging down is a reactive strategy: you buy more specifically because the price has fallen. Dollar-cost averaging (DCA) is a systematic strategy: you invest a fixed dollar amount at regular intervals regardless of price. DCA reduces timing risk and emotional decision-making; averaging down requires a judgment call about whether the price decline is temporary or reflects deteriorating fundamentals.
When averaging down makes sense - and when it doesn’t
Potentially appropriate: the company’s fundamentals are unchanged, the decline is due to broad market conditions or temporary sentiment, and you have conviction about the long-term value.
Dangerous: the price is falling because of genuine deterioration in the business (a “value trap”). Adding to a losing position in a structurally impaired company amplifies your loss. A key discipline: only average down on positions you would buy fresh at today’s price given what you know now.
Break-even price with transaction fees
The simple average cost per share formula ignores transaction fees (commissions, spreads). Including fees, your true break-even is:
Break-even price = (total cost including all fees) ÷ total shares
For example, if you paid $5 commission on each of two purchases in the worked example above ($500 + $600 + $10 fees = $1,110 total for 30 shares), your true break-even is $1,110 ÷ 30 = $37.00 - slightly higher than the unadjusted $36.67. At low commission rates ($0–$1 per trade with modern brokers), this difference is small but is worth factoring in for smaller positions.
Position size warning
Averaging down increases the concentration of your portfolio in a single position, which amplifies both potential gains and losses. Key risk management guidelines:
- Many professional portfolio managers limit any single position to 5–10% of portfolio value. Averaging down into a falling position can breach this limit quickly.
- Before adding to a losing position, calculate what percentage of your total portfolio it will represent after the new purchase.
- Consider setting a maximum additional investment rule (e.g., "I will average down at most once, and never add more than my original position size") to limit downside exposure.