What counts as a 'fair' rent increase?

“What's a fair rent increase?” is one of the most common questions renters ask when an increase arrives. The answer most articles give — “something around CPI” — is wrong. It sounds reasonable; it isn't the legal test, and tribunals do not use it.

Here's what ‘fair’ means in practice in England in 2026, and how to work out what figure is actually defensible.

There's no legal definition of a fair rent

England has no statutory definition of a “fair rent” for modern private tenancies. The Rent Act 1977 had a fair-rent framework — protected and regulated tenancies, the Rent Officer service, “ fair rent” registers. All of that is essentially closed to new tenancies. Anyone who's rented since 1989 is on an assured or assured shorthold tenancy, and the Renters' Rights Act 2025 has converted most of those into the post-RRA periodic assured tenancy.

For all of those, the test isn't ‘fair’. The test is open-market rent.

How tribunals actually decide

If a tenant challenges a Section 13 rent increase at the First-tier Tribunal (Property Chamber), the tribunal sets the rent that the property “might reasonably be expected to be let for in the open market by a willing landlord under an assured tenancy”. Section 14 of the Housing Act 1988.

This is a specific, narrow test. The tribunal looks at:

• Comparable lets in the same postcode area: similar property type, similar bedroom count, similar furnishings and condition. Several good comparables carry more weight than one.
• What's currently being asked on Rightmove, Zoopla, OpenRent and similar platforms — not historical asking prices.
• Achieved rents where they can see them — what properties actually let for, not just listed for.
• Property-specific adjustments for condition: damp, disrepair, missing services, dated kitchen/bathroom etc.

The tribunal does not consider:

• The landlord's costs (mortgage, repairs, agent fees)
• How long you've lived there
• Whether you've been a good or difficult tenant
• CPI, RPI, or wage growth
• What the property would let for if it were renovated

Why CPI isn't the test

Renters keep being told “a fair increase is something around CPI”. This is shorthand that's caught on partly because wages used to be CPI-linked, and partly because government-affordable housing rents (council and housing-association rents, social rents) are formula-linked to CPI. They're not the same market.

In the private rented sector, CPI and market rents move independently. ONS figures show periods where private rent growth ran well ahead of CPI, and others — such as late 2022, when CPI peaked above 11% — where CPI ran ahead of rent growth. A CPI-linked rise can be:

• Conservative — when the local market grew faster than CPI, the landlord is being generous
• Overshooting — when the local market grew more slowly than CPI (or fell), a CPI-linked rise pushes rent above market

Either way, the tribunal won't care what CPI did. They'll look at what comparable lets are letting for.

The lower–upper quartile framework

A practical way to think about ‘fair’ is the distribution of comparable rents in your area. For any postcode + property type + bedroom count, there's a range of rents that comparable lets are achieving. Statisticians describe that range with quartiles:

• Lower quartile (Q1): 25% of lets are below this figure. Typically older, lower-spec, or worse-condition properties.
• Median (Q2): the middle. Half above, half below.
• Upper quartile (Q3): 25% of lets are above this figure. Typically newer, refurbished, or premium-location properties.

For a tribunal-defensible increase, the rule of thumb:

• Below the lower quartile — almost certainly below market. Unusually low.
• Between lower and upper quartile — broadly market rate. Hard to challenge.
• Just above the upper quartile — possibly above market. Worth negotiating against, but tribunal may confirm.
• Well above the upper quartile — strongly above market. A challenge has a sound basis, though the tribunal decides on the evidence for your particular property.

When inflation-pegged increases happen to be fair

There's a coincidence to flag: in moderate inflation environments (say 2–4%), CPI-linked rent rises often track open-market growth reasonably well. So if your landlord proposes “rent goes up with inflation each year”, in a normal economic period it might actually land you in the market range.

This breaks down at extremes. In 2022–2023, UK CPI hit 11% while many rental markets grew more slowly. Tenants who accepted CPI-linked rises then may have paid above market. Similarly, in 2017–2019 CPI ran at around 2% while London rents were broadly flat — CPI-linked rises in that period could push rent above market.

The lesson: since the Renters' Rights Act 2025, rent review clauses — CPI-linked or fixed — can no longer be used to increase the rent. Increases have to go through a Section 13 notice (at least two months' notice, no more than once a year), which keeps the open-market route and the tribunal open to you. If you're told rent will rise automatically with inflation, check it against the Section 13 rules and keep paying your current rent until a valid notice takes effect or you agree a change.

How to calculate a fair figure for your tenancy

Five-minute version:

1. Run a check at RentCharter's rent checker. Postcode, property type, bedrooms, current rent, proposed rent. You'll get back the lower quartile, median, and upper quartile for your area. (The fair rent calculator is the same engine, framed around one question: is this rent fair?)
2. Compare the landlord's proposed figure against those three numbers.
3. If proposed sits at or above the upper quartile, your counter-offer target is the median. If proposed is between median and upper quartile, target a small reduction. If proposed is below median, it's likely already close to market — focus on other issues (repairs, condition).
4. Sanity-check against Rightmove and Zoopla: filter on your postcode and bedroom count, look at the actual listings asking those rents. The proposal should look believable next to the comparables.

Negotiating from this position

The framing matters. Don't lead with “this isn't fair” — that's subjective and your landlord will disagree. Lead with the open-market comparison the tribunal would use:

“Comparable 2-bed flats in E8 are letting for £1,750–£2,000 median £1,850 (sample of 22 lets, last 90 days). Your proposed rent of £2,200 is materially above the upper quartile. I'd like to propose £1,850.”

This is close to the framing a tribunal would use. Many landlords will recognise it and adjust. Those who don't may be betting you won't take it to tribunal — a riskier bet for them post-RRA 2025, because the tribunal can confirm or lower their figure but never raise it.

For more on the response itself, see our rent-increase response playbook with a copy-paste reply template.

Frequently asked questions