In your brokerage account, the stock is recorded as separate lots. You have one lot of 10 shares with a basis of $100 and a second lot of 10 shares at $200 basis. When you sell, you will be asked what lot you want to sell and your profit or loss will be bases on that basis.

The cost basis is $100 for 1st ten shares and $200 for 2nd ten shares. When you sell the stock the question is then which shares you sold and as B points out, irs.gov explains that completely.

$3000 invested in 200 shares = cost basis ( book cost ) $150 per share.

$150 per share average cost basis, but if you use first in first out (let's say you sell one share, the basis $100 a share; read IRS.GOV for how cost basis is determined and what is your option

Don't forget to account for your expenses

Hello all. I'm beginning to invest and have some questions about cost basis.

If I buy 10 shares of Apple at $100 a share my cost basis is obviously $100 a share. If the following year I buy 10 more shares for $200 each does my cost basis become $150? Or do the cost basis remain separate at $100 and $200.

Thanks