ISTAT Rent Index: A Practical Guide to Calculation [UPDATED]

If you have a rental agreement, ISTAT indexing is a fundamental mechanism to understand. In simple terms, it's the annual adjustment of the rent to compensate for the loss of purchasing power due to inflation. But be careful: if the contract is under the flat-rate tax (cedolare secca) regime, you can skip directly to the last paragraph, because this adjustment doesn't apply. For everyone else, this mechanism allows the landlord to update the rent based on the consumer price index (FOI index) published by ISTAT, as provided for by Art. 32 of Law 392/1978 (Art. 32) and subsequent amendments. The application varies: normally it's 75% of the variation for free-market contracts (4+4) and can reach 100% for commercial rentals or agreed-upon rents. In this guide, we'll explain step by step how to calculate it, when to notify it, and how to handle special cases.

What is the ISTAT adjustment and how does it work?

ISTAT adjustment is the tool that allows the landlord (lessor) to align the rent with the cost of living. It's not an arbitrary increase, but a mathematical revaluation based on public, official data: the FOI index (Consumer Price Index for Blue-Collar and White-Collar Worker Households), which the National Institute of Statistics (ISTAT) publishes every month.

In order to apply ISTAT rent indexing, the contract must contain a specific clause providing for it. Without this clause, the rent remains frozen.

The main rules are:

• Free-market contracts (4+4): For the most common residential rentals, the revaluation is limited to 75% of the variation in the ISTAT index.
• Non-residential (commercial) contracts and agreed-upon rents: In these cases, it's possible to apply up to 100% of the variation in the index.

Important: The golden rule is that the adjustment is a right of the landlord, but not an obligation. To make it effective, it must be formally requested from the tenant every year.

How to Calculate the ISTAT Adjustment Step by Step

Calculating the ISTAT adjustment may seem complicated, but it boils down to a simple formula. Here’s how to do it, step by step.

1. Find the Percentage Variation of the FOI Index
The key figure is the annual percentage variation of the FOI index. You can find it directly on the ISTAT website or, for convenience, in the table we've prepared further below. It's essential to use the variation between the month the contract was signed (or of the last adjustment) and the same month of the current year. A common mistake is using the old index with a 2010 base instead of the current one (2015 base).

2. Apply the Formula
The formula to calculate the increase is:

Current Annual Rent × (FOI Percentage Variation × Adjustment Percentage)

The "Adjustment Percentage" is the one specified in your contract (usually 75% or 100%).

3. Practical Example
Let's see how it works with a real example:

• Monthly rent: €600 (so €7,200 per year).
• Contract type: Free-market rent (4+4) with 75% adjustment.
• Reference month: February.
• Annual ISTAT variation (February over February): Let's assume it's +1.1%.

Now let's apply the formula:

1. Calculating the effective adjustment: 1.1% (ISTAT variation) × 75% (contract clause) = 0.825%. This is the actual percentage to apply.
2. Calculating the annual increase: €7,200 × 0.825% = €59.40.
3. Calculating the monthly increase: €59.40 / 12 = €4.95.
4. New monthly rent: €600 + €4.95 = €604.95.

Starting from the first applicable due date after notifying it, the new monthly rent will be €604.95. A similar process, based on specific indices, is also used for calculating TFR revaluation.

Table: Changes in the FOI Index (last 24 months)

To make things easier for you, here is a table showing the latest annual percentage changes in the FOI index, excluding tobacco. Find the reference month for your contract and use the corresponding value.

Reference period Percentage variation compared to the same month of the previous year

February 2026

+1.1%

January 2026

+0.8%

December 2025

+1.1%

November 2025

+1.3%

October 2025

+1.8%

September 2025

+2.1%

August 2025

+2.4%

July 2025

+2.9%

June 2025

+3.2%

May 2025

+3.8%

April 2025

+4.5%

March 2025

+5.2%

February 2025

+5.9%

January 2025

+6.3%

December 2024

+6.8%

November 2024

+7.5%

October 2024

+8.1%

September 2024

+8.9%

August 2024

+9.2%

July 2024

+9.8%

June 2024

+10.5%

May 2024

+11.2%

April 2024

+11.8%

March 2024

+12.3%

Source: ISTAT. The data is updated periodically to reflect the latest publications. For official and complete data, see the consumer price analysis.

If you manage multiple contracts, organizing the data in a spreadsheet is essential. You can start with a practical Excel table example to track deadlines and calculations.

When and how to communicate the adjustment

Have you calculated the new rent? Great. Now you need to report it correctly. A mistake here could cost you months of adjustments.

The law requires a formal notification that provides proof of receipt. The only valid methods are:

• Registered letter with return receipt (A/R): The safest and most traditional method.
• Certified Email (PEC): If both parties (landlord and tenant) have a PEC, it has the same legal value as the registered letter.

The most important rule: no retroactivity. The rent increase applies only starting from the month following the one in which the tenant receives your request. If the annual deadline is in June and the tenant receives your letter on June 2nd, the increase takes effect from the July payment. Many landlords lose months of adjustment because they don't send the notice with enough advance notice.

To keep track of your communications, you can create a log, perhaps using a spreadsheet as explained in our guide on how to create a chart in Excel.

Edge Cases You Need to Know About

Here are the answers to the most frequently asked questions about ISTAT rent indexation.

• What happens if the FOI index is negative (deflation)? Technically, the rent should decrease. However, most contracts include a clause specifying that the adjustment applies only in the case of a positive variation, to protect the landlord. Check your contract.
• Does the adjustment apply from the first year? No. The first revaluation can only be requested after the first 12 months from the contract's start date have passed.
• I forgot to request the increase for 2 years, can I recover the arrears? No, that's not possible. The right to the adjustment lapses year by year. If you don't request it, you lose the right for that period. You can only request the increase for the current year, which will be valid from the month following the notice. Case law on this point is very clear.

The exception that brings everything to a standstill: the flat-rate tax

We come to the point that makes life easier for many: the flat-rate tax (cedolare secca). The rule is simple and absolute: if as a landlord you opted for the flat-rate tax regime, you have given up any form of rent update. Period.

This means that ISTAT rent indexation does not apply for the entire duration of the option. It's a pact with the State: in exchange for reduced taxation, you commit to not increasing the rent.

If your lease is under the flat-rate tax scheme, you can completely disregard calculations, indices, and notices. The ISTAT adjustment simply does not apply to you. A request for a rent increase would be unlawful, and the tenant would have every right to refuse it.

Managing deadlines, calculations, and communications can be complicated. Data analysis platforms like Electe help turn complex data into clear reports and track every deadline effortlessly. Visit the Electe website to learn more.