The useful answer is not just the biggest increase you can ask for. It is the increase you can explain with local evidence if the tenant questions it.
Use this page when you need the search intent answered before you open the checker: what the rent increase tool checks, where the limits are, which evidence matters, and which paid Section 13 route usually fits next. The aim is to make the decision useful before you touch Form 4A or a tribunal-ready response, especially where the tenant may challenge the figure or the comparables need explaining in writing before any notice is served.
Most landlords are not looking for a theory lesson. They want to know whether the proposed rent still looks reasonable once the local market, the property details, and the chance of pushback are put together.
That is why the checker starts with comparable evidence. A figure can look fine in one set of listings and too ambitious in another, even in the same wider area.
The supportable range helps you avoid anchoring on the highest advert you can find. It shows where the stronger evidence points now, which is the figure you may need to explain later.
Once you have that range, the next step is clearer: Standard when the increase is straightforward, Defence when the figure or the tenant response makes the case more exposed.