Section 13 Rent Increase: When Does the New Rent Start?

Three Rules Govern the Effective Date

The effective date you write on Form 4A — the date the new rent starts — must satisfy three conditions simultaneously. If any one fails, the notice is invalid.

Rule 1: At least two full calendar months after service. The tenant must have a clear two-month window between receiving the notice (or deemed receipt, if posted) and the date the new rent takes effect. Two calendar months means two calendar months, not 60 days.

Rule 2: On or after the 52-week mark. The new rent cannot take effect until at least 52 weeks have passed since the tenancy started, or since the effective date of the last lawful rent increase. If rent was last increased on 15 March 2026, 52 weeks have elapsed by 14 March 2027; if the tenancy rental period starts on the 15th, the earliest aligned effective date is 15 March 2027.

Rule 3: Aligned with a rent period start date. The effective date must fall on the first day of a tenancy rental period. For a monthly tenancy where the rental period starts on the 1st, the effective date must be the 1st of a month. For a tenancy with a rental period starting on the 15th, it must be the 15th.

Working Backwards From the Date You Want

Suppose you want the new rent to start on 1 June 2027. Your tenancy started on 1 June 2026. The tenancy rental period starts on the 1st of each month.

• 52-week check: 52 weeks from 1 June 2026 is 31 May 2027. The next rental period start on the 1st is 1 June 2027. Satisfied.
• Rent period alignment: 1 June is the first day of the rental period. Satisfied.
• Two-month notice: The tenant must be served at least two full calendar months before 1 June. That means service must be complete by 1 April 2027 at the latest.

If you serve by post, deemed service is two working days after posting. Post by 30 March 2027 at the latest to ensure deemed service by 1 April, assuming no bank holiday affects the count.

In practice, post a week earlier to build in a safety buffer.

Effective Date After a Tribunal Challenge

If the tenant challenges the increase at the First-tier Tribunal, the determined rent does not take effect from your proposed date on Form 4A. It takes effect from the date of the tribunal's decision.

This is a critical distinction. If you proposed an effective date of 1 June and the tribunal issues its decision on 20 August, the new rent applies from 20 August. You continue receiving the old rent for the intervening period, and there is no mechanism to recover the difference.

Additionally, if the tribunal finds the tenant would suffer undue financial hardship from the immediate application of the new rent, it can defer the start date by up to two further months — potentially pushing the effective date to 20 October in this example.

Common Mistakes

Setting the date one day too early. If deemed service by post falls on 2 April but you wrote an effective date of 1 June, you are one day short of two full calendar months' notice. The notice is void.

Forgetting the rent period alignment. Two full calendar months from 15 January is 15 March. But if the tenancy rental period starts on the 1st, the effective date cannot be 15 March — it must be 1 April. Failing to adjust for this alignment invalidates the notice.

Counting from the service date, not the tenancy event. The 52-week rule counts from the last rent change or tenancy start, not from the date you serve the notice. Serving a notice today does not move the 52-week clock.

The 52-Week Clock for Transitional Tenancies

For tenancies that converted from an AST on 1 May 2026, the 52-week clock started from the date of the last lawful rent adjustment before conversion. If rent was increased by a contractual review clause on 1 February 2026, 52 weeks have elapsed by 31 January 2027; if the tenancy rental period starts on the 1st, the earliest aligned effective date is 1 February 2027 — even though the contractual clause itself became void on 1 May 2026.

If rent was never increased during the AST, the clock runs from the original tenancy start date.

Get the Calculation Right

The date arithmetic for a Section 13 increase — juggling postal deeming, calendar months, frequency limits, and period alignment — is where most mistakes happen. Our Section 13 rent increase guide includes a printable notice timeline planner that walks you backwards from your target effective date to the exact posting or service date, so every rule is satisfied before the notice goes out.

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