Landlords should use the Residential Tenancies Board’s current rent review notice template rather than relying on an informal letter. The notice generally needs to state the new rent, the date it takes effect, how the increase was calculated and any supporting information required under the applicable rent-setting rules. It must usually be served on the tenant and the RTB on the same day, with at least 90 days’ notice. Rules can differ for particular tenancies or exemptions, so check the latest RTB guidance or speak to a solicitor if the position is unclear.