do i claim hoh if my 21 y son lives with me. i dont claim him as a dependant

[DoninGA]

If you do not have a qualifying person as a dependent on your tax return then you cannot have Head of Household filing status.

[Hal_Al]

Q. Do i claim hoh if my 21 y son lives with me. i dont claim him as a dependant

A. No, he must be your dependent, to be a qualifying person for Head of Household filing status. 

There is one exception to that rule: If he is not being claimed, as your dependent, because his other parent (the non custodial parent) is claiming him as a dependent. Even then, it would depend on more info.