Before the Renters' Rights Act, most landlords increased rent in one of three ways: a clause in the tenancy agreement that allowed annual increases (usually CPI or a fixed percentage), an informal agreement at renewal, or a Section 13 notice on the old Form 4. All three routes were normal.

From 1 May 2026 only the third route survives, and even that has changed. The form is new (Form 4A, not Form 4), the notice period doubled, and the tribunal's powers were rebalanced toward tenants. Here's how it works now.

The three rules every increase must follow

For a Section 13 rent increase to be valid, three things must all be true. Miss any one of them and the notice is procedurally defective.

1. At least 12 months between increases

Your landlord can only increase rent once every 12 months. The clock starts on whichever is most recent: the last time the rent went up, or the start of your tenancy if it's never been increased. So if your tenancy began on 1 January 2026 and your landlord has never raised the rent, the earliest the new rent can take effect is 1 January 2027.

2. At least two months' notice

The minimum notice period under the new Act is two months between the date the Form 4A is served on you and the date the new rent takes effect. Under the old rules this was one month for most monthly tenancies; the Act doubled it. This gives you a genuine window to research market rents and decide whether to challenge.

3. Served on Form 4A

Form 4A is the prescribed form for a Section 13 rent increase on an assured tenancy in England. A landlord who sends you a letter, an email, or their own form — even if it contains all the same information — has not served a valid Section 13 notice. The form itself is on GOV.UK. The old Form 4 became invalid for any notice served on or after 1 May 2026.

Rent review clauses no longer work

This is one of the biggest practical changes. Most tenancy agreements signed before 1 May 2026 include a clause permitting the landlord to increase rent on a fixed schedule, often tied to CPI or a set percentage. Under the old system these clauses were enforceable contracts.

Under the Renters' Rights Act 2025, any contractual term in an assured-tenancy agreement that purports to allow a rent increase other than through the Section 13 procedure has ceased to have effect. Even if your contract says "rent shall increase by 5% on each anniversary", that clause is now legally void. Your landlord must use Form 4A or wait.

What "market rent" actually means

The legal test for whether a tribunal will reduce a proposed increase is whether the proposed rent exceeds the open-market rent for the property. Not a percentage. Not affordability. Not comparison to inflation. Market rent.

That means a 30% increase on a property that's deeply under-market may be unchallengeable. And a 5% increase on a property that's already at the top of the market may be challengeable. The percentage is not the question; comparable rents in your area are.

How to research market rent for your property:

• Rightmove and Zoopla— search for current listings with the same number of bedrooms, similar condition, and a similar postcode. Ignore the asking-rent figures and look at what's actually getting let.
• The ONS Private Rental Market Statistics — quarterly official figures by region, broken down by property size. Useful for a sanity check on the trajectory of rents in your area.
• Letting agent valuations— most agents will give a free informal market opinion if you ask. They're trying to win your business, so take it as one data point.

If three to five comparable properties in your postcode are renting at similar levels to your landlord's proposed figure, a tribunal challenge is unlikely to succeed. If they're consistently lower, you have a real argument.

How to challenge an increase at the tribunal

The First-tier Tribunal (Property Chamber) hears Section 13 challenges. The route is genuinely accessible: the application fee is £47 with no separate hearing fee — one of the lowest fees in HMCTS, set this low specifically to make rent challenges accessible — and Help with Fees is available if that is a problem. The application is online, and most cases are decided on paper without you ever having to attend in person.

You must apply before the proposed start date on the notice. If the proposed start date passes without you challenging, the new rent becomes payable and you can no longer challenge that particular increase.

The Renters' Rights Act 2025 changed three important things about how the tribunal works:

The tribunal can no longer set rent higher than your landlord proposed. The worst case is the rent stays where the notice says.

Under the old rules, the tribunal could determine an open-market rent that was higher than the landlord's figure, which scared most tenants out of challenging. That deterrent is now gone. The best case is the tribunal reduces it.

Backdating has been abolished.Under the old rules, if you challenged and the tribunal ruled in the landlord's favour, the new rent was backdated to the original notice date — meaning you owed arrears. From 1 May 2026, the new rent (whatever the tribunal sets it at) only takes effect from the date of the tribunal's decision.

Hardship deferral. The tribunal can defer the new rent by up to a further two months if paying it immediately would cause undue hardship. This is a safety valve for tenants who would struggle to absorb even a tribunal-approved increase straight away.

What if the rules aren't followed

A procedurally defective notice is invalid. If your landlord served the wrong form, gave less than two months' notice, or tried to increase within 12 months of the last increase, the notice has no legal effect. Your rent stays at the current level.

Your landlord can serve a new, valid notice — but they have to start the two-month clock again. So a defective notice typically costs the landlord two months of the increased rent.

You don't need to doanything to invalidate a defective notice. It's invalid by operation of law. But it's sensible to write to your landlord explaining why the notice doesn't comply, so there's no confusion about what rent is payable.

Common mistakes landlords are making

Six months into the new regime, the same defects keep coming up:

• Using a letter or email instead of Form 4A — the most common error we're seeing
• Invoking a rent review clause from the original tenancy agreement — these no longer have legal effect
• Giving one month's notice (the old minimum) instead of two
• Trying to increase rent within 12 months of the tenancy start or last increase
• Serving the old Form 4 instead of Form 4A — particularly from landlords using stationery they bought before May

Any of these makes the notice invalid. The rent stays where it is until a valid notice is served.

Where to next

If you've received a notice and want to check it, run it through our free tool. For more detail on what should be on the form itself, read Section 13 notices, decoded. For the wider context on what else changed, What changed on 1 May 2026.