By law, it is allowed to increase the rental by 20% every year. But when a landlord does that, the tenant would surely reach a point that he couldn't afford it anymore so more likely the tenant would leave. As per our experience, the increase is moderate at 10% and not every year but every 2 years. At least we felt that the landlord somehow cared for their tenants. Salaries here do not increase every year so landlords should understand that an increase in rent is a big blow to the finances of the tenant.