Average Down & Cost Basis Calculator
Add each purchase to get your average cost per share, total invested, and unrealized P&L. You can also solve for how many shares to buy at today's price to bring your average down to a target.
| Shares | Price ($) | Fees ($) |
|---|
How to use
- Enter each purchase: shares, price, and any fees. Click + Add purchase for more rows.
- Enter today's price to see market value and unrealized P&L.
- Enter a target average to see how many more shares you would need to buy at today's price.
Formulas explained
Worked example Hypothetical
Hypothetical: 100 shares at $50 plus 100 at $40 = 200 shares at an average of $45. At $30, getting to a $40 average needs 200 × (45 − 40) / (40 − 30) = 100 more shares ($3,000).
FAQ
Is averaging down a good idea?
It lowers your breakeven, but it also increases your exposure to a position that is falling. Many traders limit it or avoid it entirely.
Does this match my tax cost basis?
Brokers usually track tax lots individually (FIFO, specific ID). The average shown here is a planning figure.
Can I use it for crypto or ETFs?
Yes. It works for anything bought in units.
Average down calculator explained for beginners
What this tool does
It shows your new average cost per share when you buy more of a stock you already own, and how many shares it would take to bring your average down to a target.
What each input means
- Current price
- What the stock trades at now, the price you would pay for new shares.
- Target average
- The average cost per share you would like to reach.
- Shares, price and fees (each row)
- One row per past purchase: how many shares you bought, the price per share, and any fee.
How to read the results
Your average cost is total dollars spent divided by total shares. Buying more at a lower price lowers that average, but it also puts more money into the same stock.
A short worked example (hypothetical)
You own 100 shares at $50 ($5,000). The stock is at $40. Buying 100 more for $4,000 brings you to 200 shares for $9,000, an average of $45.
Common mistakes
- Averaging down only to feel better about a losing position without checking why the price fell.
- Ignoring how large the position becomes compared with your account.
- Forgetting fees in the cost basis.