How to calculate a rent increase from RPI, CPI or a percentage

In England, Wales, Scotland and Northern Ireland, the calculation is only half the job: the rent increase must also use the correct statutory notice route for that nation. For private residential lets, RPI, CPI and percentage calculators do not by themselves make a rent rise valid.

How do you calculate a rent increase?

You calculate a rent increase by multiplying the current rent by the chosen percentage, then serving the correct notice for the nation: in England use the section 13 process, in Wales use section 123, in Scotland use a PRT rent-increase notice, and in Northern Ireland give at least 3 months’ written notice for most private tenancies. The basic rent increase formula is current rent × (1 + percentage ÷ 100), so £1,000 per month increased by 5% becomes £1,050 per month; the same formula works in Excel, a yearly rent increase calculator, or a monthly rent increase calculator. The legal process differs: England’s government guidance says, “You need to follow the section 13 process every time you increase the rent, even if you have already agreed the increase with your tenants.” Wales requires at least two months because “The period between the day on which the notice is given to the contract-holder and the specified date may not be less than two months.” Scotland allows no more than one rise in 12 months, and Northern Ireland requires the new rent date to be at least 3 months after notice. Abodient can record the new rent figure, the notice served and the date it takes effect against the tenancy, so the rent roll across a portfolio stays accurate once an increase lands rather than needing a manual update.

How much can you increase the rent by?

In England, Wales, Northern Ireland and most of Scotland, there is no general private-rent percentage cap, but the rent must still survive the relevant notice, challenge and market-rent rules. In England, the Renters’ Rights Act position is not a rent-control cap: government says, “The government does not support the introduction of rent controls, and nothing in the Act restricts landlords raising rents in line with market prices.” If a tenant challenges an English section 13 increase, the tribunal tests open-market rent and may set “the open-market rent, if lower than the proposed rent”. Wales section 123 sets notice and timing rather than a percentage ceiling. Scotland’s ordinary PRT position is clear government guidance: “There is no cap on how much you can increase rent by.” That changes only in a designated Scottish rent control area, where increases will be limited to CPI plus 1%, capped at 6%; no such area is operating yet, with first local authority rent reports due no later than 31 May 2027. Northern Ireland’s temporary rent-freeze power expired after 28 October 2023.

What is a reasonable annual rent increase, and how much have rents actually risen?

A reasonable annual rent increase in 2026 is best benchmarked against ONS market data: UK average private rent rose 3.7% to £1,393 in the 12 months to July 2026, with England at 3.8%, Wales 4.5%, Scotland 1.7% and Northern Ireland 2.3% to May 2026. ONS says, “Average UK monthly private rent increased by 3.7%, to £1,393, in the 12 months to July 2026 (provisional estimate); this annual growth rate is up from 3.3% in the 12 months to June 2026.” For the nations, ONS records: “Average rents increased to £1,451 (3.8%) in England, £843 (4.5%) in Wales, and £1,016 (1.7%) in Scotland, in the 12 months to July 2026.” Northern Ireland was lower: “In Northern Ireland, average rents increased to £875 (2.3%), in the 12 months to May 2026.” Zoopla’s 2.1% and HomeLet’s 3.4% are useful new-let indicators, but they are not equal alternatives to the ONS stock measure because they track new lets rather than all private rents.

How do you calculate an RPI rent increase?

For a private residential tenancy, an RPI rent increase clause does not raise the rent by itself: in England the landlord must still use section 13, in Wales section 123, in Scotland the PRT rent-increase notice rules, and in Northern Ireland written notice under Article 5E. England’s section 13 rule is explicit that a contrary tenancy term is ineffective where rent increases otherwise than by notice, determination or agreement: “any provision relating to an assured tenancy to which this section applies is of no effect so far as it provides that the rent for a particular period of the tenancy must or may be greater than the rent for the previous period otherwise than by virtue of a notice, determination or agreement mentioned in this subsection.” For commercial leases in England and Wales, the Court of Appeal formula in Monsolar was last year’s rent × current RPI ÷ prior RPI, using the RPI figures two months before each review date. Do not copy that commercial RPI rent calculator formula into residential lettings: residential rent is tested through the statutory process and, in England, against open-market rent.

How do you calculate a CPI rent increase?

For a private residential tenancy, there is no general statutory CPI rent increase formula in England, Wales, Scotland or Northern Ireland; CPI matters only where the law or the contract specifically makes it matter, and the residential statutory notice process still controls the increase. In England’s private rented sector, a CPI clause does not replace the section 13 process or the open-market test. The clearest statutory CPI formula is social housing, where the Rent Standard defines CPI as “the percentage change in the CPI in the 12 months to the September falling in the preceding financial year.” That is why England’s 2026–27 social rent guideline is September 2025 CPI of 3.8% plus 1%, or 4.8%, but that is not a private-landlord CPI rent increase calculator. Scotland’s future rent-control-area rule will use CPI plus 1%, capped at 6%, because Scottish Government guidance says applicable PRT increases in a rent control area “will be limited to the Consumer Price Index (CPI) plus 1%, up to a maximum of 6%.” The CPI rate itself was 2.9% in July 2026.

Is CPI or RPI better for a rent increase?

CPI is usually the better benchmark for a fair residential rent increase, while RPI has historically produced higher increases and is weaker as an official inflation measure. The UK Statistics Authority’s position is unusually direct: “We have been clear that the RPI is not a good measure, at times significantly overestimating inflation and at other times underestimating it, and have consistently urged all – in Government and the private sector – to stop using it.” In July 2026, RPI was still higher than CPI: ONS reported that “The annual RPI inflation rate was 3.2% in July 2026,” while CPI rose by 2.9%. That 0.3 percentage-point gap in one month is small, but it compounds over long leases; Forsters calculated that on a £1m 10-year lease from 2012, using RPI rather than CPI produced nearly £95,000 of extra rent. For private residential rent, the practical answer is simpler: whichever index is named in the agreement, the increase still has to pass the national statutory route and any market-rent challenge.

How do you calculate a commercial rent increase?

You calculate a commercial rent increase by applying the rent-review machinery in the lease; no UK-wide statute supplies a default mid-term percentage formula for commercial leases. If the lease says open-market rent, valuation evidence drives the answer; if it says RPI or CPI indexation, the formula usually applies the index movement to the passing rent; if it says fixed uplifts, the arithmetic is whatever the lease states. For England and Wales renewals under the Landlord and Tenant Act 1954, the court-set rent is open-market rent: the Act refers to rent “at which, having regard to the terms of the tenancy… the holding might reasonably be expected to be let in the open market by a willing lessor”. That Act does not cover Scotland or Northern Ireland because “This Act shall not extend to Scotland or to Northern Ireland.” In Northern Ireland, the Lands Tribunal renewal regime is not capped by the 1978 rent-control order, and in Scotland a sheriff renewing a shop tenancy may set “such rent… as he shall, in all the circumstances, think reasonable.”

How does a cap and collar change an index-linked rent review?

A cap and collar turns an index-linked rent review into a three-step calculation: work out the indexed rent, lift it to the collar if it is too low, and cut it back to the cap if it is too high. For example, if rent is £100,000 and the RPI formula gives 8% but the lease has a 5% annual cap, the reviewed rent is £105,000, not £108,000; if the index gives 1% but the collar is 2%, the rent becomes £102,000. On multi-year reviews, caps and collars usually compound: Hill Dickinson gives the practical warning that “a 2% per annum collar becomes a chunkier 10.4% if the rent is only being reviewed every 5 years, while the 5% per annum cap becomes a whopping 27.6%.” In England and Wales, future rent-review controls are not generally in force yet, but once commenced they will make terms ineffective where they push passing rent above the statutory reference amount: “The rent review terms are of no effect to the extent that they would result in the new passing rent being larger than the reference amount.” No equivalent Scotland or Northern Ireland cap-and-collar rule is in force.

Last reviewed August 2026.

Sources

• GOV.UK, assured tenancy agreements guide, rent increases — “You need to follow the section 13 process every time you increase the rent, even if you have already agreed the increase with your tenants.” Source
• Housing Act 1988 section 13 — “For the purpose of securing an increase in the rent under a tenancy to which this section applies, the landlord may serve on the tenant a notice in the prescribed form proposing a new rent to take effect at the beginning of a new period of the tenancy specified in the notice, being a period beginning not earlier than—” Source
• Housing Act 1988 section 13 — “(b)in any other case, the date that falls 52 weeks after the date on which the increased rent took effect.” Source
• Renting Homes (Wales) Act 2016 section 123 — “The period between the day on which the notice is given to the contract-holder and the specified date may not be less than two months.” Source
• Private Housing (Tenancies) (Scotland) Act 2016 section 22 — “The landlord under a private residential tenancy may increase the rent payable under the tenancy by giving the tenant a notice in accordance with this section (“a rent-increase notice”).” Source
• Private Housing (Tenancies) (Scotland) Act 2016 section 19 — “The rent payable under a private residential tenancy may not be increased more than once in a 12 month period.” Source
• Private Tenancies (Northern Ireland) Order 2006 Article 5E — “The date specified under paragraph (3)(a) must be not less than 3 months after the date on which the notice is given to the tenant.” Source
• GOV.UK, Guide to the Renters’ Rights Act — “The government does not support the introduction of rent controls, and nothing in the Act restricts landlords raising rents in line with market prices.” Source
• Housing Act 1988 section 14ZB — “(a)the open-market rent, if lower than the proposed rent, and” Source
• mygov.scot, landlord rent increases — “There is no cap on how much you can increase rent by.” Source
• Housing (Scotland) Act 2025 section 23 — “(b)6%.” Source
• Scottish Government, rent controls — “The first report from each local authority is due no later than 31 May 2027.” Source
• Department for Communities Northern Ireland, Private Tenancies Act sections 7–12 — “This deadline passed on 28 October 2023.” Source
• ONS, Private rent and house prices UK: August 2026 — “Average UK monthly private rent increased by 3.7%, to £1,393, in the 12 months to July 2026 (provisional estimate); this annual growth rate is up from 3.3% in the 12 months to June 2026.” Source
• ONS, Private rent and house prices UK: August 2026 — “Average rents increased to £1,451 (3.8%) in England, £843 (4.5%) in Wales, and £1,016 (1.7%) in Scotland, in the 12 months to July 2026.” Source
• ONS, Private rent and house prices UK: August 2026 — “In Northern Ireland, average rents increased to £875 (2.3%), in the 12 months to May 2026.” Source
• Zoopla, Rental Market Report — “This is a rise of 2.1% or £30 in the last year.” Source
• HomeLet Rental Index — “This figure is 3.4% more expensive than in July 2025.” Source
• Housing Act 1988 section 13 — “any provision relating to an assured tenancy to which this section applies is of no effect so far as it provides that the rent for a particular period of the tenancy must or may be greater than the rent for the previous period otherwise than by virtue of a notice, determination or agreement mentioned in this subsection.” Source
• Monsolar IQ Ltd v Woden Park Ltd [2021] EWCA Civ 961 — “On the true construction of the Lease, paragraph 3 of Schedule 6 to the Lease means that the rent passing at the end of each complete year of the term is to be increased or decreased on the Review Date in accordance with any proportionate change in the RPI during that year, as measured by the values of the RPI two months before the Review Date and two months before the previous Review Date (or, in the case of the first Review Date, two months before the Term Commencement Date).” Source
• Rent Standard 2026 — “‘CPI’ means the general index of consumer prices (for all items) published by the Office for National Statistics or, if that index is not published for any month, any substituted index or index figures published by that Office; and where this Rent Standard refers to CPI this is a reference to the percentage change in the CPI in the 12 months to the September falling in the preceding financial year.” Source
• Ipswich Borough Council, Council Housing Rents 2026–27 — “This is the September 2025 CPI rate of 3.8% plus 1% as per the Government’s Rent Settlement Agreement, which was extended for a further 10 years from 1 st April 2026 in the Government’s 2025 Autumn Statement.” Source
• Scottish Government, rent controls — “In a rent control area, rent increases for applicable properties which are let under private residential tenancies will be limited to the Consumer Price Index (CPI) plus 1%, up to a maximum of 6%.” Source
• ONS, Consumer price inflation: July 2026 — “The Consumer Prices Index (CPI) rose by 2.9% in the 12 months to July 2026, up from 2.6% the previous month.” Source
• UK Statistics Authority statement on the future of the RPI — “We have been clear that the RPI is not a good measure, at times significantly overestimating inflation and at other times underestimating it, and have consistently urged all – in Government and the private sector – to stop using it.” Source
• ONS, Consumer price inflation: July 2026 — “The annual RPI inflation rate was 3.2% in July 2026.” Source
• Forsters, CPI or RPI — “If our lease was granted for a term of 10 years in 2012 (conveniently avoiding the spike in inflation in 2022) and with a starting rent of £1,000,000 exclusive, then linking to RPI rather than CPI would result in nearly £95,000 of additional rent being paid over the term.” Source
• Landlord and Tenant Act 1954 section 34 — “The rent payable under a tenancy granted by order of the court under this Part of this Act shall be such as may be agreed between the landlord and the tenant or as, in default of such agreement, may be determined by the court to be that at which, having regard to the terms of the tenancy (other than those relating to rent), the holding might reasonably be expected to be let in the open market by a willing lessor, there being disregarded—” Source
• Landlord and Tenant Act 1954 section 70 — “This Act shall not extend to Scotland or to Northern Ireland.” Source
• Business Tenancies (Northern Ireland) Order 1996 Article 18 — “None of the provisions of the [1978 NI 20.] Rent (Northern Ireland) Order 1978 shall operate to limit or affect the amount of the rent which may be fixed by the Lands Tribunal under paragraph (2).” Source
• Tenancy of Shops (Scotland) Act 1949 section 1 — “On any application under the foregoing subsection the sheriff may, subject as hereinafter provided, determine that the tenancy shall be renewed for such period, not exceeding one year, at such rent, and on such terms and conditions as he shall, in all the circumstances, think reasonable, and thereafter the parties shall be deemed to have entered into a new lease of the premises for that period, at that rent and on those terms and conditions.” Source
• Hill Dickinson, Five FAQs: index-linked rents — “Just remember that the collar and cap need to be compounded if the rent is not being reviewed annually, so that a 2% per annum collar becomes a chunkier 10.4% if the rent is only being reviewed every 5 years, while the 5% per annum cap becomes a whopping 27.6%.” Source
• Renters’ Rights Act 2026 schedule 37 — “The rent review terms are of no effect to the extent that they would result in the new passing rent being larger than the reference amount.” Source