As a landlord, I prefer to only raise the rent at the end of a lease. So if it's 6 months or 12 months - that's the tenants choice. We go by RE recommendation. I've also been a renter & had the rent upped on us mid-way through a 12 month lease. We were p'd off & ended up breaking our lease because of it (in part). So if they were only on a 6 month lease then ok but if it's mid way - no increase. It's business, & they will understand.