Rent increase calculator (UK): CPI, RPI and room by room

A free rent increase calculator for UK landlords. Put in the current rent and pick a percentage, the latest CPI or RPI, or the new rent you have in mind. It shows the new rent, the increase a month and a year, and, for each room in an HMO, the earliest date a section 13 increase can start in England.

Luke AshtonFounder of Bricky Bot and Based Lettings · Updated 25 October 2026

How to calculate a rent increase

There are three ways landlords arrive at a figure, and the calculator does all three. Whichever you use, compare the £ a month with what similar rooms let for before you propose it.

A yearly figure depends on how the rent is paid: a monthly rent × 12, a weekly rent × 52, a four-weekly rent × 13. A £150-a-week room going up 4% is £6 a week, £312 a year. Rounding the new rent down to the pound keeps it at or under the percentage, which reads better on a notice than £646.88.

CPI, CPIH or RPI: which index to use

The Office for National Statistics publishes all three each month. These are the 12-month rates for September 2026, published on 21 October 2026; the next figures are due on 18 November 2026, and this page is updated when they are.

An index is a sensible yardstick: if your bills, insurance and repairs have gone up about as much as prices generally, a CPI-sized rise keeps the rent where it was in real terms. But it isn’t a rule. A private tenancy in England can’t be index-linked any more (see below), and the tribunal, if the tenant asks it, looks at the market rent for the home, not at inflation. Use the index to sense-check a figure, not to set it.

How much can a landlord increase rent?

In England there is no cap on the amount. What limits it is the process in section 13 of the Housing Act 1988, as amended by the Renters’ Rights Act 2025, and the tenant’s right to challenge:

• One way to do it. Since 1 May 2026, a section 13 notice on Form 4A is the only way to raise the rent on a private assured tenancy. GOV.UK’s landlord guide says to use it even when the tenant has already agreed. Rent review clauses in tenancy agreements no longer work.
• The tribunal sets the market rent. The tenant can apply to the First-tier Tribunal before the new rent starts (£47 fee). It decides what the home would let for on the open market on the same terms; the result can be lower than you proposed but not higher, and isn’t backdated (s.14ZB).
• So the real limit is the market. A rise well above what similar rooms let for invites a challenge you would lose, and a tenant who leaves. A rise in line with the market and your costs is the one that sticks.

When the new rent can start

The calculator gives each room’s earliest start date from the day the tenants get the notice. Every limit is “not earlier than”, so the latest one wins, and then the date moves on to the next first day of a rent period:

• Two months after the tenant gets the notice.
• 52 weeks after the tenancy’s first rent period began: no increase in the first year.
• 52 weeks after the last increase took effect, or 53 when the 52-week dates have crept more than six days ahead of the anniversary of the first increase (the calculator uses the last increase for that check; our section 13 notice template asks for both dates).

Example: a notice reaches the tenant on 2 November 2026. A room whose tenancy began on 1 February 2025 can go up from 1 February 2027 (two months is 2 January, and the rent day is the 1st). A room that began on 19 September 2025 can go up from 19 January 2027. A room whose last increase was on 1 March 2026 has to wait until 1 March 2027.

Rent increases in an HMO: room by room

In a shared house each room let is its own tenancy, with its own rent, start date and history. That changes three things:

• One notice per room, each with its own date. Serve them together if you like, but the rooms may go up on different days. The three rooms in the calculator, all served on 2 November 2026, start on 19 January, 1 February and 1 March 2027.
• The same percentage isn’t the same rise. At CPI the three rooms go from £1,875 to £1,940.63 a month between them: £21.00, £22.75 and £21.88. Tenants compare notes in a shared kitchen, so think about whether a flat £ rise per room is easier to explain.
• Bills-inclusive rent. If the room rent includes energy, water, broadband or council tax, part of the increase is bills, and Form 4A’s question 4.7 asks you to show each charge now and proposed. Our council tax checker gives this year’s bill for the house.

Before you settle on figures, check what the house returns at the new rents in the HMO rental yield calculator, and what an agent would take of them with the property management fees calculator.

Index-linked rent and rent review clauses

• From 1 May 2026, they have no effect on a private assured tenancy in England. A clause saying the rent goes up by RPI, CPI or a fixed amount each year can’t raise the rent; GOV.UK says an increase agreed before then that takes effect after it won’t apply.
• Clause increases before 1 May 2026 still count for the 52-week rule: the next section 13 increase can’t start until 52 weeks after one took effect. Enter it as the last increase.
• New agreements should say that rent increases follow section 13. Our tenancy agreement template does.
• Ground rent and commercial leases follow their own lease terms and law. This calculator is for residential tenancies.

Wales and Scotland

• Wales: a notice of variation of rent, form RHW12, under the Renting Homes (Wales) Act 2016: two months’ notice, at most once a year. The percentage sums are the same; the start dates in the calculator are for England.
• Scotland: a rent-increase notice with three months’ notice; the tenant can refer it to a rent officer.

What Bricky Bot does (and doesn’t)

Bricky Bot is the HMO management software we built to run our own rooms: an AI lettings team that answers enquiries, handles WhatsApp and repairs, and keeps compliance and rent in order, with a person approving every message before it goes to a tenant. It doesn’t write or serve rent increase notices, and it doesn’t remind you when a rent review is due. It keeps the figures this calculator needs:

• Each tenancy’s current rent, start date and rent day.
• A monthly rent account per tenancy, worked out from your bank statement lines. When the rent changes, past months keep the amount that was due then.

Questions landlords ask

Sources

• Office for National Statistics: CPI annual rate (D7G7), CPIH annual rate (L55O), RPI 12-month change (CZBH); September 2026, released 21 October 2026
• Housing Act 1988, section 13 (as amended by the Renters’ Rights Act 2025) and section 14ZB
• GOV.UK: Assured periodic tenancies, a guide for landlords: rent increases
• GOV.UK: Apply for an open-market rent determination
• Checked 25 October 2026.