The practical answer for England: for a private-rented-sector assured periodic tenancy, a landlord must serve a completed Form 4A at least two months before the proposed new rent starts. That is only the starting point. The first increase cannot begin until 52 weeks after the tenancy began; later increases are generally subject to a 52-week rule, and the new rent must start at the beginning of a tenancy period. A rent review should protect income and protect the relationship.