What this calculator does
If you bought shares of a stock or fund at different times and prices, your average cost per share is the total you paid divided by the shares you own. Enter each purchase, the price now and, if you like, the price of a new purchase and the average you want, and the calculator shows your average cost, your gain or loss, and how many shares you would need to buy to reach that average.
How it is worked out
Average cost = (shares × price + commission, added up for every purchase) ÷ total shares. Example: 10 shares at $50, 20 at $40 and 10 at $30 cost $1,600 for 40 shares, an average of $40. At $35 a share they are worth $1,400, a $200 loss. To bring the average to $38 by buying at $30, you would need (1,600 − 38 × 40) ÷ (38 − 30) = 10 more shares, costing $300.
Average cost and taxes
When you sell, your gain or loss for taxes is figured from your cost basis. For stocks, unless you identify which shares you sell, the IRS generally treats the first shares you bought as the first ones sold. The average-cost method can be used for shares of mutual funds and certain other shares, under IRS rules (IRS Publication 550). Your broker reports cost basis on Form 1099-B.
Frequently asked questions
How do I calculate my average cost per share?
Add up what you paid for every purchase, including commissions, and divide by the total number of shares you own.
What does averaging down mean?
Buying more shares at a lower price, which lowers your average cost. It does not change the risk of the investment, and the price can keep falling.
Is my average cost the same as my tax cost basis?
Not always. For stocks, tax rules usually match the shares you sell with specific purchases, first in, first out unless you choose. Your broker's records and Form 1099-B show your cost basis.
Is my information saved?
No. The numbers stay on this page.