Usually, when signing for 12 months, you are responsible for all 12 months. I asked this exact question of a prospective landlord, and he said that I would be responsible for all 12, or until he got a new tenant. For instance, if I decided to leave after 6 months, and he rented it right away, I wouldn't owe him anything more. But If it takes him another 2 months to get another tenant in, I'd have to pay for those two months I didn't use it. Hope this helps you.