The Residential Tenancies Act allows the landlord to increase the rent once a year. For monthly periodic tenancies, landlords are required to provide three tenancy months written notice of the increase in rent. This means that if the landlord wanted the rent increase to start on January 1, the landlord would have to serve the rent increase notice before October 1. For weekly tenancies, landlords must provide 12 weeks notice and for any other periodic tenancies, landlords must provide 90 days notice.
For fixed term tenancies, the landlord can only increase the rent once per year, and can only increase once the term is over. For example, if there was a one year fixed term tenancy, the landlord could increase the rent at the end of the fixed term, to be effective for the next fixed term tenancy.
If there was a six month fixed term tenancy, the landlord could not increase the rent at the end of that fixed term because 365 days have not passed since the tenant began renting there. If they entered into a another 6 month fixed term tenancy after the first one, then the landlord could increase the rent at the end of the second lease.
The landlord does not have to provide written notice of a rent increase in a fixed term tenancy situation. It is a very good idea for the tenant and the landlord to talk to one another about what will happen at the end of the fixed term, and if the landlord is going to raise the rent. This conversation should be held at least one month before the end of the tenancy.