Calculate Your Average Stock Price in Seconds
Bought shares at different prices? Enter each purchase and instantly see your average cost per share, total invested, break-even price, and current profit or loss.
What Is a Stock Average Calculator?
A stock average calculator — sometimes called an average down calculator or cost basis calculator — works out your average purchase price per share when you have bought the same stock multiple times at different prices. This figure, known as your cost basis per share, is the number that determines whether you are in profit or at a loss on a position.
Every time you add to a stock position, your average price shifts. Buying more shares at a lower price brings your average down (averaging down). Buying at a higher price pushes it up (averaging up). Tracking this manually across multiple trades gets tedious fast — our calculator handles it instantly, no matter how many purchases you have made.
How to Calculate Average Stock Price
The formula is simple — but it trips people up because you cannot just average the prices. You must account for how many shares you bought at each price.
// where Total Amount Invested = Σ(shares × price per share)
// You break even when market price = your average cost
Worked Example — Averaging Down
Say you bought shares in a company three times as the price fell. Here is how the average cost calculation works:
| Purchase | Shares | Price | Total Cost |
|---|---|---|---|
| Buy 1 — Jan | 100 | £50.00 | £5,000 |
| Buy 2 — Feb | 150 | £38.00 | £5,700 |
| Buy 3 — Mar | 200 | £27.00 | £5,400 |
| Total | 450 shares | — | £16,100 |
Average cost per share = £16,100 ÷ 450 = £35.78 · Simple average of prices = (£50 + £38 + £27) ÷ 3 = £38.33 (incorrect — ignores share quantities)
The simple average of the three prices (£38.33) is wrong because you bought twice as many shares at £27 as at £50. The correct average cost — weighted by share quantity — is £35.78. That is your break-even price, and it is what matters for your P&L.
What Does Averaging Down Mean?
Averaging down is the act of buying additional shares in a stock after its price has fallen below what you originally paid. Because the new shares are purchased at a lower price, your average cost per share decreases. This means the stock does not need to recover all the way back to your original entry price for you to break even — it only needs to reach your new, lower average.
- You buy 100 shares at £60 — your average cost is £60.00.
- The stock falls to £40. You buy another 100 shares.
- You now hold 200 shares. Total invested: £10,000. Average cost: £50.00.
- The stock only needs to reach £50 for you to break even — not £60.
Averaging Down — Pros and Cons
Averaging down is a tool, not a strategy in itself. Whether it makes sense depends entirely on why the stock fell and whether the underlying business case remains intact.
✓ When it works well
- The stock fell on broad market weakness, not company-specific problems
- You have done your research and the fundamentals remain strong
- You are investing for the long term with a clear thesis
- It reduces the price level needed to break even or profit
- You have position sizing discipline and are not over-concentrating
✗ When it goes wrong
- The business is in genuine long-term decline
- You are averaging down on emotion rather than analysis
- The position already represents too large a share of your portfolio
- You lack the capital to sustain further drops
- The original investment thesis no longer holds
Important: Averaging down does not change the underlying value of the business — it only changes your entry price. If a stock is falling because the company’s prospects are deteriorating, buying more shares multiplies your exposure to a declining asset, not a recovering one. Always re-examine your original thesis before adding to a losing position.
Average Up vs Average Down
Most investors hear about averaging down, but averaging up — buying more shares as a stock rises — is equally valid and often more profitable over the long run. When a stock is rising, it typically means the market is confirming your original thesis. Adding to a winning position increases your exposure to a trade that is already working.
The choice between the two depends on your conviction, position size, and time horizon. Our calculator handles both scenarios equally — simply enter each purchase, whatever the price direction, and the correct average is calculated automatically.