按比例享受免税额。一般拿不满50万。

Let's say you rented out the house for 8 years, and lived as primary resident for 2 years before sale.  and You made 500K capital gain. 

8/10 of the gain is taxable (400K taxable gain).  only 2/10 of the gain qualifies for primary residency exclusion. (100K exclusion)