Index-Linked Rent Review Calculator
Calculate your new index-linked rent from RPI or CPI figures, with cap, collar and upwards-only rules applied and shown step by step.
Calculator Inputs
Breakdown
| Step | Calculation | Result |
|---|---|---|
| Index ratio | Enter both index figures above | - |
| Per-annum equivalent | Based on index ratio and review period | - |
| Final rent | Current rent × applied ratio | - |
Scenario Analysis
| Scenario | New Rent | Change |
|---|---|---|
| Your result | - | - |
| Pure index-linked (no cap/collar/floor) | - | - |
| Index +1 percentage point per annum | - | - |
| Index −1 percentage point per annum | - | - |
Index-Linked Rent Review Process
Review date arrivesThe date set in the lease's rent review clause is reached.
Obtain the published index figuresThe base figure fixed at the last review, and the current figure for the month the lease specifies, both from the ONS.
Apply the formulaIndex ratio, then any collar, cap and upwards-only rule set out in the lease, in that order.
Notify the other partyA memorandum or letter recording the new rent is usually exchanged, even though the calculation itself is formulaic.
Resolve any disagreementDisputes on an index-linked review are rare since the figures are published, but usually turn on which month's index or which clause wording applies.
New rent takes effectOften backdated to the review date itself, with any shortfall for the gap period settled once agreed.
What Is An Index-Linked Rent Review?
An index-linked rent review resets the rent using a fixed formula tied to a published inflation index — usually RPI or CPI — rather than a surveyor's opinion of the current market rent. The lease fixes a base index figure (typically the reading at the last review or lease start) and, at each review date, the new rent is the current rent multiplied by the current index figure divided by that base figure. Because both figures are official published numbers from the Office for National Statistics, the calculation itself rarely needs a surveyor or valuation, which is the main reason landlords and tenants use it in preference to an open-market review.
RPI vs CPI: Which Index Applies, And Why It Matters
RPI (Retail Prices Index) runs from a January 1987 = 100 base and CPI (Consumer Prices Index) from a 2015 = 100 base — the two series measure inflation differently and are not interchangeable, so only the ratio between two dates of the same series is valid for a review. RPI lost its designation as a National Statistic in 2013 over methodological concerns, but it is still specified in a large share of existing commercial lease drafting; CPI and CPIH have become more common in newer leases. Your lease names exactly one index — using the wrong one, even for the right month, produces the wrong new rent.
How Caps And Collars Work
A cap sets a maximum increase the tenant will pay regardless of how high the index rises; a collar sets a minimum increase the landlord will receive regardless of how low the index falls. Both are usually expressed as a percentage per annum and compounded over the number of years since the last review — a 4% per annum cap over a 3-year review period allows up to roughly 12.5% (1.04³), not a flat 12%. Commercial lease commentary describes collar/cap pairs commonly set around 2–4% per annum, built around an assumed typical increase of roughly 3% a year (Myerson Solicitors, "Different Types Of Rent Reviews In Commercial Leases"). Wider pairs also exist: Colliers has described a 7% cap used against a 10% annual index reading during a higher-inflation period (Colliers, "If the rent cap fits, bear it").
The 2030 RPI-CPIH Alignment
The UK Statistics Authority's published reform plan has RPI's monthly growth rates matching CPIH's from February 2030, with the two series' annual rates fully aligned from February 2031. CPIH typically runs lower than RPI historically, so a lease with reviews falling after February 2030 and an RPI-linked clause may see smaller increases from that point on than the same clause would have produced under RPI's pre-reform methodology — worth flagging to whoever manages a long lease with reviews spanning that date.
Common Mistakes When Calculating An Index-Linked Review
The most common error is using the wrong month's index reading — leases specify an exact month for both the base and current figures, and the ONS publishes a new figure every month, so picking the reading for the review date itself rather than the month named in the clause gives a wrong answer. Others include applying a cap or collar as a flat figure over the whole review period when the clause actually compounds it per annum (or the reverse), forgetting that RPI and CPI figures cannot be mixed even for the same property, and missing that most UK commercial reviews are upwards-only so a falling index should not be read as a rent cut unless the clause explicitly allows it.
Method And Limits
This calculator applies the index-ratio, cap, collar and upwards-only formula exactly as entered — it does not look up ONS figures for you, and it does not know your specific lease's drafting. It deliberately does not model: reviews where the cap or collar is expressed as a fixed £ amount rather than a percentage; reviews where the cap/collar applies to the whole review period as a single figure rather than compounding per annum (some older leases do this — check your clause's exact wording); stepped or tiered indexation; or VAT and service charge adjustments that sometimes accompany a rent review letter. It also does not determine which specific month's index reading your lease requires — that is fixed by the clause, not by this tool. Figures and formulas checked 2026-09-15.
Frequently Asked Questions
What's the difference between RPI and CPI for a rent review?
They are different statistical series with different base years (RPI: January 1987 = 100; CPI: 2015 = 100) and different methodologies. RPI lost its status as a National Statistic in 2013 over methodological concerns, but it remains widely used in existing lease drafting. Some newer leases specify CPI or CPIH instead. Your lease clause names one specific index — using figures from the wrong one will produce the wrong rent.
Where do I find the RPI or CPI figure for my review date?
The ONS publishes both indices monthly, typically around the third week of the month following the one being measured (for example, the October 2025 reading was published on 19 November 2025), at ons.gov.uk. Your lease will specify exactly which month's published figure counts as the base and which counts as the current figure for each review.
What happens if the index has actually fallen?
Enter the lower current index figure as normal — the ratio comes out below 1. If your lease has a collar, that sets the floor and the rent still rises by at least the collar amount. If there is no collar but the review is upwards-only, the rent stays the same rather than falling. Only a lease with no collar and no upwards-only wording would let rent actually fall — check the clause carefully before assuming that applies to you.
Is an index-linked review the same as an open market rent review?
No. An open market review resets the rent to whatever a hypothetical letting would achieve on the open market at the review date, usually requiring a surveyor's valuation or, in a dispute, an independent expert or arbitrator. An index-linked review is a fixed formula applied to published index figures, so it is faster and cheaper to calculate but does not track actual local market rent changes.
Do residential tenancies use index-linked rent reviews?
Rarely in the same form. Most assured shorthold tenancy rent increases in England use a Section 13 notice under the Housing Act 1988 or a contractual rent review clause tied to a fixed amount or percentage, not an RPI/CPI-linked formula with caps and collars — that structure is overwhelmingly a commercial lease feature.
Sources
- ONS – Inflation and price indices (RPI and CPI, published monthly)
- UK Statistics Authority – statement on the future of the RPI (2030/2031 CPIH alignment)
- Practical Law – indexed rent review clause based on RPI subject to cap and collar
- Myerson Solicitors – different types of rent reviews in commercial leases
- Colliers – if the rent cap fits, bear it
Last updated: 2026-09-15. This page gives an estimate only and is not legal, tax, financial, or employment advice.
About this tool
Created and maintained by CoryVu. Read how we check our tools and consult the sources and assumptions on this page.
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