Section 13 Rent Increase Calculator (Renters’ Rights Act 2025)

Section 13 of the Housing Act 1988 has always been the statutory mechanism for raising rent on a periodic assured or assured shorthold tenancy where the tenancy agreement does not contain a contractual rent-review clause. Until now most landlords ignored it: a fixed-term AST could simply be re-issued at a higher rent, or a Section 21 notice could be served if the tenant refused. From 1 May 2026 the Renters’ Rights Act 2025 abolishes Section 21 and converts every assured shorthold into a periodic assured tenancy with no fixed-term renewal. From that date, Section 13 is the only lawful route to a rent increase.

The Renters’ Rights Act 2025 also strengthens the procedural and substantive protections around Section 13. The notice period extends from one month to two months. The 12-month gap rule (no more than one Section 13 increase in a 12-month period) is preserved. The prescribed Form 4 is mandatory — a non-prescribed letter or email is invalid even if the rent figure is correct. Most importantly, the First-tier Tribunal can no longer set rent above the figure proposed in the Section 13 notice; it can only confirm or reduce. Pre-RRA the tribunal could award a higher rent than the notice if the market supported it, which in practice deterred tenants from referring borderline increases. Post-RRA the tribunal becomes a one-way ratchet in the tenant’s favour and referral risk goes up.

The two-month notice clock starts on the day the notice is properly served, not the day it is signed or posted. First-class post adds two working days for service under section 7 of the Interpretation Act 1978 (deemed service); recorded delivery adds the same; email service is only valid where the tenancy agreement specifically permits it. The earliest possible effective date is the next rent payment date that falls at least two months after deemed service. The calculator handles both the deemed-service offset and the next-rent-day rounding so the date in the notice is the date the tribunal will accept.

Pricing the proposed rent is now a tribunal-risk decision rather than a contractual freedom. The tribunal’s test under section 14 of the Housing Act 1988 is open-market rent for an assured tenancy of the property at the relevant date, ignoring tenant improvements, tenant-caused dilapidations and the existence of the current tenant. In practice the tribunal looks at advertised rents on Rightmove, Zoopla and SpareRoom for comparable properties in the same postcode, adjusted for void allowance and condition. Pitching the Section 13 figure within 95% of credible market evidence makes referral pointless for the tenant; pitching above market triggers a referral and a tribunal-set rent that becomes the new ceiling for the next 12 months.

The 12-month gap rule deserves particular attention because it interacts with the new periodic-only regime. Once a tenancy converts on 1 May 2026, the first Section 13 must respect a minimum 52-week interval from the most recent rent change — whether that change was a previous Section 13, a re-issued AST at a higher rent, or even an agreed mid-tenancy increase by deed. Landlords whose tenants signed a fresh AST in early 2026 at an uplifted rent therefore cannot re-increase under Section 13 until the same date in 2027. The calculator surfaces this 12-month-since check and rejects notices that violate it.

Operationally the new regime turns rent-pricing into a quarterly portfolio decision rather than a renewal-event decision. Best practice is to track the next-allowable Section 13 date per tenancy, review market rents 60 days before, and serve at the right point in the cycle to maximise compounded yield while staying inside the tribunal-safety zone. Inside LetCompliance the same calculator output feeds the dashboard’s rent-review ladder and pre-fills the prescribed Form 4 PDF for one-click service.