Stock Average Calculator (Average Down Calculator)
By Santaji GadepatilinUpdated October 27, 2026
When you buy more of a share at a different price, your average cost changes. Knowing it tells you your break-even price. This free stock average calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the stock average calculator
Enter the number of shares and price for each purchase (up to three). The calculator shows total shares, total invested and the average price per share. Leave the third purchase at zero if you only bought twice.
To plan a purchase, type your target average in Average price and press × on the second purchase shares — the calculator finds how many to buy at the new price.
Stock average formula
Average price = (q₁p₁ + q₂p₂ + q₃p₃) ÷ (q₁ + q₂ + q₃)
Example: averaging down
| Purchase | Shares | Price | Cost |
|---|---|---|---|
| First | 100 | 250 | 25,000 |
| Second | 50 | 200 | 10,000 |
| Total | 150 | 233.33 | 35,000 |
The share now needs to rise only to 233.33 to break even, instead of 250.
Shares needed to reach a target average
Starting with 100 shares at 250, buying at 200:
| Target average | Extra shares needed |
|---|---|
| 240 | 25 |
| 235 | 43 |
| 230 | 67 |
| 225 | 100 |
| 220 | 150 |
| 210 | 400 |
The closer the target is to the new price, the more shares you need — the cost rises steeply.
Averaging down vs averaging up
- Averaging down: buying more as the price falls, lowering your average.
- Averaging up: buying more as the price rises, often used by momentum investors.
Both increase your position size. Set a maximum allocation per stock before you start.
Tax lots
For capital gains tax, many systems use first in, first out (FIFO) to decide which shares were sold. Your average cost and your tax cost basis may differ — check local rules.
Frequently asked questions
How do I calculate the average price of shares?
Total amount invested ÷ total shares. 100 shares at 250 plus 50 at 200 is 35,000 ÷ 150 = 233.33.
How many shares do I need to buy to reach a target average?
Enter the target as the average price and press × on the second purchase quantity. The calculator solves for the shares needed at the new price.
Is averaging down a good idea?
Only if your reasons for owning the stock still hold. Averaging down lowers your break-even price but increases your exposure to a falling share.
Do brokerage and taxes change the average?
Yes. Add brokerage, exchange charges and stamp duty to the price paid for an accurate cost basis.