Hal_Al
Level 15

Get your taxes done using TurboTax

Q.  Can I be a cosigner on him renting a room or will that count as 'support'? 

A. Co-signing does not count as support, you provided.

 

Filing an independent tax return is a pretty minor item in feeling independent.  He gains nothing tax wise, but you lose the (up to) $500 Other dependent tax credit and possibly some earned income credit.