Capital gains basis for stock

[ironlog]

Bought stock for my child at age 5 and put it into an account for him with me as custodian until he turned 21 years old. His social security number has always been on the account. At age 22 he sold some of the stock for about $4000. For income tax on capital gains calculation, is the basis of the stock the price when I set up the account or the price when he turned 21 because that is when he had control over it?