For most landlords this is the rule that bites soonest. The Section 8 possession reform is consequential but slow-burning (the first court cases on the new grounds are only now landing). The tenancy-form conversion happened in a single moment on 1 May 2026 and is essentially complete. The rent-increase reform is the rule a landlord will actually exercise next, the first time they want to raise the rent on a tenancy at its annual anniversary. This page walks the operational mechanics of that next rent-rise, the tribunal challenge route the tenant now has, and the section 24 cash-flow tightening that the interaction with mortgage interest produces.

The statutory anchors: amended Section 13 of the Housing Act 1988 (mechanism for rent rises), amended Section 14 of the Housing Act 1988 (tribunal determination), Section 6 of the Renters' Rights Act 2025 (statutory procedure for increases), Section 7 of the RRA 2025 (challenging amount or increase, including the new no-overshoot rule), and SI 2026/421 (commencement on 1 May 2026). The companion pages are the AST-to-periodic conversion mechanics page (which sets up the tenancy form into which Section 13 operates), the possession guide (which covers Ground 8 rent arrears as the enforcement route if rent is not paid), and the enforcement-defence guide (which covers the marketing-compliance breaches that overlap with rent-rise decisions).

Why Section 13 is now the only route

The Renters' Rights Act 2025 amended Section 13 of the Housing Act 1988 to provide that, for assured tenancies, the rent can only be increased through: (a) a section 13(2) statutory notice on the prescribed form, (b) an agreement between landlord and tenant under section 13(4)(b), or (c) a tribunal determination on a section 13 / section 7 application. Any contractual rent-review clause purporting to increase the rent outside these three channels is unenforceable. The index-linked clauses (annual RPI or CPI uplifts), the fixed-percentage escalators (annual 3% or 4% increases written into the original tenancy agreement), and the open-market review clauses common in higher-end PRS lettings are all overridden.

The single-channel rule is one of the most significant operational changes for portfolio landlords. Many pre-2026 BTL tenancy agreements built in an index-linked review as a low-friction way of raising rent automatically each year; under the new regime, those clauses cannot be used and the landlord has to serve a positive section 13(2) notice each year on the prescribed form with a defensible market figure.

The once-per-12-months and 2-month rules

Two interlocking constraints. First, a section 13 notice can only take effect at most once in every 12-month period. The first permitted increase date is 52 weeks after the start of the tenancy; subsequent permitted increases are at least 52 weeks after the previous one. A landlord who serves a notice each year on the tenancy anniversary will see a steady annual escalation; a landlord who skips a year does not bank an additional increase opportunity and simply restarts from the new anniversary point.

Second, the notice itself must give at least 2 months from service to the proposed increase date (up from 1 month for monthly tenancies under the old rules). For a tenancy with a 1 August anniversary, the practical workflow is to serve the section 13(2) notice in early June at the latest, with the proposed increase date of 1 August. A late-served notice (June 15, with proposed increase date of August 1) is invalid because the 2-month minimum is not met; the landlord has to push the proposed increase date out to mid-August or serve again next year.

The prescribed form and what it must contain

The section 13(2) notice must be on the prescribed form (Form 4 under the assured-tenancy forms regulations as amended by RRA 2025 supplementary instruments). The form requires: the property address, the current rent, the proposed new rent, the start date of the new rent (at least 2 months after service), the names and addresses of landlord and tenant (the agent if expressly authorised to serve), a tenant-rights information block explaining the right to apply to the First-Tier Tribunal Property Chamber under section 14, and the signature and date of service.

A handwritten letter, an email summary, or any communication that does not use the prescribed form is not a valid section 13(2) notice and cannot have the effect of raising the rent. The landlord who relies on an informal communication and starts demanding the higher figure is exposed to a rent-arrears defence by the tenant (the higher rent was never lawfully fixed), to potential complaints to local-authority rent-officer teams in some boroughs, and (if the informal route is used systematically across a portfolio) to the prospect of a section 7 initial-rent challenge being raised against every new tenancy in the portfolio.

The tribunal challenge route under amended Section 14

If the tenant disputes the proposed rent, they apply to the First-Tier Tribunal Property Chamber on the prescribed form (Application for the tribunal to decide a new rent) before the increase date in the section 13(2) notice. The application must be made in time; a late application normally extinguishes the right to challenge for that particular rent rise.

If the application is made in time, the proposed increase is suspended pending tribunal determination. The tenant continues paying the existing rent until the tribunal decides. The hearing typically falls 8 to 12 weeks after application, often decided on paper without an oral hearing where the evidence is documentary. The tribunal's determination is the open-market rent for the property on a hypothetical comparable basis (the comparable test), capped at the landlord's proposed figure.

The no-overshoot rule, the structural change in tenant incentives

Under the pre-2026 regime, a tribunal determining a rent challenge could in principle set the rent above the landlord's proposed figure if the market evidence supported it. The risk that the tribunal might raise the rent further deterred many tenants from challenging modest proposed increases. Section 7 of the RRA 2025 removed that risk: the tribunal cannot now set the rent above the amount the landlord proposed in the section 13(2) notice. The worst-case outcome for the challenging tenant is the landlord's proposed amount; the best-case outcome is a lower amount if the market evidence supports it.

The implication for landlords is asymmetric. A modest, defensible proposed increase (say, in line with local market comparables) is unlikely to be challenged because the tenant has limited upside (a few pounds per month) and full transaction cost (form-filling, evidence preparation, possible attendance). An aggressive proposed increase that meaningfully exceeds market evidence is much more likely to be challenged because the tenant has substantial upside and the same fixed transaction cost. The pattern that emerges in tribunal data over the first six months of the new regime is that challenges concentrate on the high-percentage-increase cohort and on landlords with multiple proposed increases across the same building or street.

The separate 6-month initial-rent challenge under Section 7

Section 7 of the RRA 2025 also created a separate, narrower tenant right to challenge the initial rent (the rent fixed at the start of the tenancy, not a later increase). The challenge is brought to the FTT Property Chamber on the same comparable-market test as a section 13 challenge, with the same no-overshoot rule. Three distinguishing features.

  • Available within 6 months of the tenancy start, once per tenancy.
  • The challenge is to the initial contracted figure, not to an increase notice. There is no statutory notice that triggers the window; the tenant can simply apply within the 6-month window.
  • The contracted rent continues to be payable during the tribunal process; any tribunal-ordered reduction takes effect from the date of application, not from the start of the tenancy.

For landlords advertising property to a new tenant under the new regime, the practical implication is that the agreed rent figure has to be defensible against market evidence at the point of marketing. An aggressively-priced new tenancy is exposed to a tribunal reduction at month 6 even if the tenant accepted the figure at the outset. The marketing-compliance regime under Chapter 6 Part 1 (covered on our separate marketing-compliance page later in this series) operates in parallel and limits how far the advertised rent can be pushed during the marketing period.

What the tribunal looks at: the comparable evidence pack

The tribunal applies a comparable-market test. The standard evidence package on both sides (tenant-applicant and landlord-respondent) typically includes:

  • Rightmove / Zoopla / OnTheMarket listings for comparable properties in the same locality (typically within 0.5 to 1 mile, same bedroom count, similar age, similar condition) at the date of the proposed increase. Screenshots with date stamps and listing URLs are the standard evidential format.
  • Let-agreed evidence from the same letting agent or from local managing agents where available. This is the strongest form of evidence because it shows what the market actually transacted at, not what landlords are asking for.
  • Local-authority rent statistics from the borough or unitary authority, often published quarterly in the housing-strategy data.
  • LHA rates for the broad rental market area (BRMA) as an informational floor reference, particularly in cases involving tenants in receipt of housing benefit or Universal Credit housing element. Not determinative but informationally relevant.
  • Improvements and deteriorations since the last rent was fixed (new bathroom, replaced kitchen, deteriorated condition, council enforcement notice on the way). Photographic evidence and invoices form the documentary trail.

The tribunal typically determines on the basis of the documentary evidence; oral hearings are now uncommon for routine section 13 challenges. Both parties can request an oral hearing but it adds 4 to 6 weeks to the timeline and is rarely the proportionate route for a £30 to £100 per month rent dispute.

The Section 24 cash-flow interaction

For individual landlords (not companies) the Section 24 mortgage interest restriction means mortgage interest is not deductible against rental income; it is restricted to a 20% basic-rate tax credit under section 274A ITTOIA 2005. The interaction with the section 13 once-per-year cap is structural: rent rises slowly under the section 13 framework, but interest costs can rise quickly (variable-rate mortgages, fixed-rate expiries refinancing into higher rates).

Worked example. Mrs Patel owns a let property in the south-east. Rent £1,800 per calendar month. Mortgage £280,000 at 4.5% interest-only, monthly interest £1,050. In 2026/27 her gross rent is £21,600, interest is £12,600, other property costs £2,400. Net rental profit before tax: £6,600. Tax on £6,600 at 40% (assuming higher-rate band): £2,640. S24 credit: 20% of £12,600 = £2,520. Net tax cost £120. After-tax cash flow: £6,600 - £120 = £6,480.

Suppose her fixed-rate mortgage expires in August 2026 and she refinances at 5.5%. New monthly interest £1,283; annual interest £15,400. Her existing rent is set by a section 13 notice she could only serve in June 2026 to take effect 1 August 2026. The maximum permitted increase to that rent is once per 12 months, and the market-defensible figure is say £1,920 (a 6.7% increase). Annual rent rises to £23,040. Net rental profit: £23,040 - £15,400 - £2,400 = £5,240. Tax at 40%: £2,096. S24 credit: 20% of £15,400 = £3,080 (capped at the tax otherwise payable on rental income, so effectively £2,096). Net tax cost: nil. After-tax cash flow: £5,240.

Despite the rent rise, Mrs Patel's after-tax cash flow has fallen by £1,240 because the section 13 cap means her rent could not keep pace with the interest cost increase. This is the structural cash-flow tightening that the rent-cycle reform imposes on geared landlords. Our section 24 case study covers the portfolio-level mechanic; the structural response (incorporation, debt-pay-down, sale) involves separate trade-offs that need modelling.

A worked Section 13 timeline

Mr Hassan lets a one-bed flat in a regional city. Tenancy started 1 March 2025, rent £950 per calendar month. The tenancy converted to periodic on 1 May 2026. The first permitted section 13 increase is 52 weeks from tenancy start, i.e. 1 March 2026, but Mr Hassan has not raised the rent yet and decides to do so for the 2026/27 cycle effective 1 December 2026 (when his annual review historically falls).

Local market evidence: comparable one-beds in the same area letting at £1,020 to £1,100 per month based on Rightmove listings April to October 2026 (8 comparables). Mr Hassan settles on £1,050 as a defensible figure (mid-range, 10.5% increase). He serves the section 13(2) notice on the prescribed form on 25 September 2026 with proposed increase date 1 December 2026 (9-week notice, safely above the 2-month minimum).

The tenant receives the notice on 27 September. She is not minded to challenge (the new rent remains below the upper end of the local market) and pays the higher figure from 1 December 2026. Next section 13 notice can be served any time after 1 October 2027 with a proposed increase date no earlier than 1 December 2027 (52 weeks from the effective date of the previous increase).

Alternative branch: the tenant disputes the figure and applies to the FTT Property Chamber on 15 November 2026 (15 days before increase date, within the window). The proposed increase is suspended; the tenant continues paying £950 pending hearing. Tribunal lists the matter on paper for 22 January 2027. Mr Hassan files the comparable-evidence pack on 8 January; tenant files her counter-pack on 12 January. Tribunal determines the open-market rent at £1,020 (lower end of the comparable range, accepting some condition discount). Effective date 1 December 2026 per the original notice. Mr Hassan receives the difference (£70 x 2 months = £140) plus the prospective £1,020 monthly. Total time from notice to determination: 18 weeks.

Practical takeaway for the next rent-rise cycle

Three operational points. First, build the evidence pack before serving the notice, not after the challenge lands. The comparable-market work is the same work either way; doing it upfront sets the proposed figure at a defensible level and prevents the wasted-month outcome of a successful challenge reducing the increase. Second, observe the once-per-12-months and 2-month rules as hard constraints, not negotiable points; a defective notice cannot be cured and means waiting another year. Third, model the section 24 interaction at the property level before pricing the rent rise; the section 13 cap means the rent has to do the work of recovering interest-cost increases that, in cash-flow terms, are not deductible.

Adjacent reading: our landlord tax changes 2026 pillar for the wider regulatory context; our RRA tax-implications page for the deeper section 24 interaction discussion; our first-time landlord pillar for the operating framework.