Glossary
Retail Prices Index (RPI)
Short answer
The Retail Prices Index (RPI) is a UK measure of inflation published monthly by the Office for National Statistics (ONS). It is labelled "Not a National Statistic" and sits alongside CPI and CPIH. It remains widely written into older UK contracts, so clauses should name the exact index.
By Pactinel editorial teamReviewed on October 22, 2026
The UK publishes several inflation measures: CPI, CPIH and RPI. RPI is the oldest and has long been used in commercial leases, service contracts and some loan documents. The ONS publishes RPI time series on its inflation and price indices pages and marks them as not being a National Statistic.
Why precision matters
RPI and CPI generally produce different annual rates for the same period. A clause that says "inflation" or "the retail price index" without more can lead to disputes, particularly in contracts written many years ago.
What to specify
- The index and series (RPI all items, with the series ID if one is used).
- The base month and comparison month.
- A fallback if RPI is changed or ceases to be published.
- A cap, if the parties want to limit exposure.
Example clause
"The rent will increase on each anniversary by the percentage rise in the RPI (all items) over the 12 months ending three months before the review date, subject to a maximum of 4% and a minimum of 0%."
This example combines a lag with a cap and floor. See cap and floor.
When reviewing older contracts, check whether the named index still exists in the form the clause assumes. See also CPI and indexation.
This is general information, not legal advice.