Invalid Section 13 notice: the mistakes to avoid

An invalid Section 13 notice means the rent increase has no effect, and the tenant carries on paying the old rent. The mistakes below come from the Housing Act 1988 and the notes on Form 4A, and each one is avoidable: the wrong form, a start date that breaks one of the three date rules, missing tenants or signatures, and no proof of service.

What makes a Section 13 notice invalid?

This table sets out the mistakes that can make a Section 13 notice invalid, based on the statute and the Form 4A notes. It is not an official list, and the last item is a risk rather than a settled rule.

#	Mistake	Why it matters	How to avoid it
1	Using old Form 4, a letter, an email or a home-made template	Only Form 4A is the prescribed notice for private tenancies	Download Form 4A from GOV.UK each time
2	Changing the prescribed wording	GOV.UK: "If you change the wording, the form may not be valid"	Fill in the blanks only
3	Less than two months between service and the start date	s.13(2)(a) requires at least two months	Count from service, not signing; allow for the post
4	Start date not on the first day of a rent period	Form 4A Note A	Match the day (monthly) or weekday (weekly) the periods begin
5	Start date within 52 weeks of the tenancy start or last increase	s.13(2)(b)	Count any pre-May 2026 clause increase; check the 53-week rule
6	A joint tenant left out, or no proof of service	Note 1.1; you must be able to evidence service	Copy names from the agreement; keep a service record
7	A rent period longer than a month	Rent periods must be a month or less (s.4A; Note 4.1)	State the period as it runs now
8	Not every joint landlord signs	Form 4A requires all to sign, or one on behalf of all	Get every signature, or sign on behalf of all
9	Wrong figures in the service charges and bills table (question 4.7)	Effect on validity isn't settled	Treat it as a risk and check the figures twice

Wrong form or changed wording

Since 1 May 2026, Form 4 is for social housing only, and the form itself says "Do not use this form if the property is rented privately". A rent increase letter, an email, or a clause in the tenancy agreement can't do the job either. Any term allowing the rent to rise other than through Section 13 or a tribunal decision is of no effect.

Changing the form is just as risky. GOV.UK says: "Do not change the wording of these forms unless the form says you can." Don't delete notes, merge pages or add conditions. If you want to explain the increase, send a separate covering letter, like our rent increase letter template. Our Form 4A guide explains where to download the current version.

Date mistakes

Most of the rules on a Section 13 notice are about the start date in question 4.6. These are the traps:

• Counting from the wrong day. The two months run from service. Counting from the date you signed the form is a listed mistake.
• Posting without a margin. If the tenant receives the notice a few days later than you planned, a start date that was exactly two months away may now be short.
• Ignoring the rent day. On a monthly tenancy that began on the 20th, the new rent must start on the 20th, not the 1st.
• Forgetting an earlier increase. A rent review clause or Form 4 increase that took effect before 1 May 2026 starts the 52-week clock (SI 2026/421 reg 7).
• Missing the 53-week rule. On weekly and fortnightly tenancies, the 52-week date drifts earlier each year. If it would fall more than six days before the anniversary of the first increase after 11 February 2003, you must wait 53 weeks.

Example of a near miss. A monthly tenancy began on 15 September 2023, rent due on the 15th. The landlord signs Form 4A on 10 October 2026, intending a start date of 15 December 2026, and posts it on 14 October. If the tenant receives it on 16 October, two months from service is 16 December 2026, so 15 December is too early. The safe start date is 15 January 2027.

The rent increase notice period page has a calculator that applies all three rules.

People and signature mistakes

• Every joint tenant must be named (Note 1.1). Copy the names from the tenancy agreement, including anyone who has moved out but is still a tenant.
• Every joint landlord must sign, or one signs on behalf of all. A form signed by one of two co-owners, without saying it's on behalf of both, is a risk.
• You must be able to prove service. Use the method in your tenancy agreement if it sets one. Otherwise hand it over, leave it at the property, or use registered post. Email only if the agreement allows it. Record the date, time and method.

Rent period and bills table mistakes

Rent periods must be 28 days or shorter, or monthly. If your agreement still says quarterly or yearly, the tenancy has run on monthly periods since 1 May 2026, and the form should reflect that. Read periodic tenancy rent increases to find your current rent day.

Question 4.7 is a table for service charges and bills included in the rent. Whether an error there invalidates the notice isn't settled, so treat it as a risk. Fill it in with accurate figures.

What happens if you serve an invalid Section 13 notice?

• The increase has no effect. The old rent remains the lawful rent.
• The tribunal can decide validity. If the tenant applies on form MR1, the tribunal can rule on whether the notice is valid (s.13B).
• Don't count the increase as arrears. Possession grounds for arrears count only rent "lawfully due", and rent from an unlawful increase may not count. See what to do if a tenant refuses a rent increase.
• Start again with a new notice. Serve a fresh Form 4A and work out every date from the new service date. That means at least two months' delay, and the new start date must still be a rent day.

What to do next

• Avoid every mistake on this list by letting us fill in Form 4A and check the dates, free with a ValidNotice account: start from the Section 13 notice page.
• Follow our how to fill in Form 4A walkthrough if you're completing the form yourself.