ISTAT Rent Adjustment: How It Works and How to Calculate It [2026]

If you are a tenant or a landlord, every year you face the same question: the ISTAT rent adjustment. How much does the rent increase? How is it calculated? Can the landlord apply it automatically? In this complete guide, we analyze the ISTAT revaluation mechanism, the applicable percentages based on the type of lease, and how to perform the correct calculation with practical examples updated for 2026.

What is the ISTAT rent revaluation

The ISTAT revaluation is the mechanism that allows the lease rent to be updated based on changes in the cost of living, as measured by the consumer price index published by ISTAT (the Italian National Institute of Statistics).

The purpose is simple: to protect the landlord's purchasing power. If inflation is 2%, a rent of 500 euros today "is worth" less next year. The revaluation compensates for this loss of value.

The adjustment is not automatic: it must be stipulated in the lease agreement and, in most cases, the landlord must formally notify the tenant.

The FOI index: the reference parameter

The index used for rent revaluation is the FOI (consumer price index for Blue-Collar and White-Collar Worker Households), excluding tobacco products. ISTAT publishes it monthly in the Official Gazette and on its website.

Please note: there are several ISTAT indices (NIC, HICP, FOI). For rental adjustments, only the FOI excluding tobacco is used.

The percentage change in the FOI is calculated by comparing the index of the reference month with that of the same month in the previous year. For example, if the FOI for January 2026 is 120.5 and January 2025 was 118.2, the change is:

(120.5 - 118.2) / 118.2 × 100 = 1.94%

This 1.94% is the basis for calculating the adjustment. But be careful: it is not always applied at 100%.

75% or 100%: which percentage applies?

The applicable ISTAT adjustment percentage depends on the type of lease:

The general rule for residential leases is 75%. The 100% rate can only be applied if the lease contains an explicit clause providing for the full adjustment. In the absence of any clause, no adjustment is possible.

Practical example with 75%

Current monthly rent: 700 euros
Annual FOI change: 2.40%
Applicable percentage: 75%

Calculation:

1. Applicable change: 2.40% × 75% = 1.80%
2. Monthly increase: 700 × 1.80% = 12.60 euros
3. New rent: 700 + 12.60 = 712.60 euros per month
4. Annual increase: 12.60 × 12 = 151.20 euros more per year

Practical example with 100%

Same rent and same change, but with a 100% clause:

1. Applicable change: 2.40% × 100% = 2.40%
2. Monthly increase: 700 × 2.40% = 16.80 euros
3. New rent: 700 + 16.80 = 716.80 euros per month
4. Annual increase: 16.80 × 12 = 201.60 euros more per year

The difference between 75% and 100% in this case is 50.40 euros per year. For an instant, error-free calculation, use our ISTAT rent revaluation calculator: enter the current rent and the ISTAT change, and get the new amount in seconds.

4+4 vs 3+2 leases: differences for the revaluation

Open-market rent lease (4+4)

In a 4+4 lease, the rent is freely set between the parties. The 75% ISTAT revaluation applies annually starting from the second year. The landlord sets the initial rent without restrictions, and the adjustment serves to keep it in line with inflation.

Regulated-rent lease (3+2)

In a 3+2 lease, the rent is determined based on local agreements between landlord and tenant associations. The initial rent is generally lower than the free market, but the landlord enjoys significant tax benefits:

• 30% reduction of the IRPEF taxable base (or flat-rate tax at 10%)
• Variable IMU (property tax) reduction depending on the municipality
• Reduced registration tax

For the 3+2 lease as well, the ISTAT revaluation applies at 75%, unless a different contractual clause states otherwise.

When and how the adjustment is applied

When it takes effect

The ISTAT adjustment applies from the anniversary of the lease. If the lease was signed on April 1, 2024, the first possible adjustment is from April 1, 2025, the second from April 1, 2026, and so on.

The FOI index to use is generally that of the last available month before the anniversary date, or of the previous month if the current one has not yet been published.

Notification to the tenant

The landlord must notify the tenant of the ISTAT adjustment request. This notification:

• Must be in written form (registered letter with return receipt, certified email/PEC, or even a simple letter)
• Must indicate the FOI index used, the percentage applied, and the new amount
• Takes effect from the month following receipt (unless different contractual provisions apply)

Important: if the landlord does not request the adjustment, the tenant is not required to pay it voluntarily. However, the landlord can request arrears for the past 5 years (statute of limitations).

Example of an adjustment notification letter

A proper notification should contain:

• The lease details (signing date, registration)
• The FOI index for the reference month of the current and previous year
• The calculated percentage change
• The percentage applied (75% or 100%)
• The increase amount and the new monthly rent
• The effective date of the new amount

Cumulative revaluation or year by year?

A common question concerns the basis for calculating the revaluation when it has not been applied for one or more years. There are two methods:

Year-by-year method (correct)

The adjustment is always calculated on the previous year's rent (already revalued), not on the original rent. This creates a compounding effect.

Example over 3 years with an initial rent of 600 euros and FOI changes of 2%, 1.5%, and 2.5%:

• Year 2: 600 + (600 × 2% × 75%) = 600 + 9 = 609 euros
• Year 3: 609 + (609 × 1.5% × 75%) = 609 + 6.85 = 615.85 euros
• Year 4: 615.85 + (615.85 × 2.5% × 75%) = 615.85 + 11.55 = 627.40 euros

If the landlord has never requested the adjustment

If for some years the landlord did not request the revaluation, they can still claim arrears within 5 years. The arrears calculation is performed by applying the revaluation year by year based on the FOI index for each period.

The flat-rate tax (cedolare secca) and ISTAT revaluation

A fundamental point: those who opt for the flat-rate tax regime (cedolare secca) (a fixed rate of 21% for open-market leases or 10% for regulated-rent leases) waive the ISTAT revaluation for the entire duration of the option.

This means that if the landlord chooses the flat-rate tax, the rent remains unchanged for the entire lease term (4 or 3 years + renewal). It is a choice that should be carefully considered: does the tax savings from the flat-rate regime compensate for giving up the ISTAT adjustment?

Comparison example

Rent: 800 euros/month. Average inflation: 2% per year.

With flat-rate tax (cedolare secca, 21%):

• Annual income: 9,600 euros
• Taxes: 9,600 × 21% = 2,016 euros
• No ISTAT revaluation

With standard IRPEF (marginal rate 35%) and revaluation:

• Annual income (with 5% deduction): 9,120 euros
• Taxes: 9,120 × 35% = 3,192 euros
• But ISTAT revaluation: +12 euros/month in the second year, increasing thereafter

In this case, the flat-rate tax is more advantageous despite giving up the adjustment, because the tax savings (over 1,100 euros per year) far exceed the foregone revaluation. But for very high rents or with high inflation, the calculation could change.

What to do if inflation is negative

In the case of deflation (negative FOI change), the rent should theoretically decrease. However, in contractual practice, many leases contain a clause providing for adjustment "only in the case of positive change." In the absence of such a clause, the landlord should reduce the rent.

In Italy, significant deflation occurred only in 2014-2016, with very small negative changes (around -0.1% / -0.5%).

How to use the calculator

Our ISTAT rent revaluation calculator allows you to calculate the new rent in just a few clicks. Simply enter:

• The current monthly rent
• The percentage change in the FOI index
• The applicable percentage (75% or 100%)

The calculator instantly returns the new monthly amount, the increase in euros, and the annual total, eliminating any risk of calculation errors.

Frequently asked questions

Is the ISTAT adjustment mandatory?

No, it is not mandatory. It is a right of the landlord that must be actively exercised through written notification to the tenant. If the landlord does not request it, the tenant does not have to pay it. Furthermore, it must be provided for in the lease agreement.

Can the tenant refuse the adjustment?

If the adjustment clause is present in the lease and the landlord has properly communicated the revaluation with references to the ISTAT indices, the tenant cannot refuse. In case of dispute, the landlord can take legal action through an injunction order to obtain the unpaid differences.

Where can I find the updated FOI index?

The FOI index is published monthly on the ISTAT website (www.istat.it) in the "Prices" section. It is generally made available around the 15th of the month following the reference month. It is also published in the Official Gazette.

Is the revaluation calculated on the original rent or on the already revalued rent?

The revaluation is always calculated on the previous year's rent, which may have already been revalued. This creates a "compound interest" effect that, over the course of a long lease, can lead to significant rent increases.

Can I apply the ISTAT adjustment with the flat-rate tax (cedolare secca)?

No. Choosing the flat-rate tax regime involves an explicit waiver of the ISTAT revaluation for the entire duration of the option. If the landlord wants to apply the adjustment, they must return to the standard IRPEF regime, which is possible at the annual expiration of the flat-rate tax option.

How is the adjustment communicated to the tenant?

The notification must be in writing. The recommended methods are: registered letter with return receipt (the safest from an evidentiary standpoint), certified email (PEC) (if both parties have a certified address), or a hand-delivered letter with a signed receipt. The notification must include the FOI index, the percentage applied, the new amount, and the effective date.