Compare the increase as both a euro amount and a percentage, then check the local rents for similar properties using the RTB Rent Register. Regional market differences may explain why rents vary, but location alone does not automatically make an increase lawful. Check the tenancy start date, the rent-control rules and exceptions that apply, and whether the landlord gave the required notice and supporting information. If you believe the increase breaches the rules, the RTB can decide a dispute based on the tenancy’s facts; a solicitor can advise on a particularly complex case.