The Harmonised Indices of Consumer Prices (HICP) measure the changes over time in the prices of consumer goods and services acquired by households. They give a comparable measure of inflation as they are calculated according to harmonised definitions.

The RTB RPZ calculator shall compare the HICP value contained in the HICP table published by the RTB on or most recently before the date that the rent was last set, with the HICP value contained in the HICP table published by the RTB on or most recently before the date that any new rent increase is being determined by the calculator.

Any difference between the two aforementioned HICP values shall be calculated as a percentage by the RPZ calculator. If that percentage is a positive value (i.e. there has been an increase in HICP values over the period in question), it is applied by the RPZ calculator to the amount of the rent last set to produce the amount of any permissible rent increase.

If that percentage is zero or a negative value, the calculator will advise that no rent increase is allowed. This does not prevent a landlord and a tenant agreeing a lower rent than the current rent. Any table of HICP values published by the RTB shall be based on the All-Items Harmonised Index of the Consumer Price (HICP) values in relation to Ireland, which is published by the Central Statistics Office with reference to EuroStat data.

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