LMNP and SIRET: mandatory or not in 2026?

Updated March 29, 2026 - The short answer is yes: as soon as you start a non-professional furnished rental activity, you must declare that start and obtain a SIRET number. The key point is not whether you are a "small landlord" or a "large landlord", but whether your activity is formally registered. In 2026, the DGFiP is unambiguous on this requirement.

In practice, an LMNP without a SIRET is not a normal situation. It typically means an incomplete file and a source of downstream errors on the CFE, the professional space, the annual tax package or the start-of-activity formalities. If you rent out a furnished property, treat it as a fully declared activity — even if you remain non-professional in the tax sense.

A SIRET is mandatory in LMNP because it formally identifies your furnished rental activity. It underpins the déclaration of your start of activity, connects your file to a professional space if required, and secures the tax obligations that follow.

The impôts.gouv.fr sheet updated on January 27, 2026 specifies that whether you are a non-professional or professional furnished landlord, you must declare the creation or start of activity within 15 days following the first day of rental. This formality is completed online at the formalities counter (guichet des formalités), which generates a SIRET number.

To complete, see LMNP tax, LMNP tax package and CFE LMNP.

The SIRET is used to:

• officially register the activity;
• choose or declare the applicable tax régime;
• create a professional online space if required;
• meet certain mandatory reporting obligations.

In LMNP, it connects your furnished rental to a coherent tax and administrative framework.

A simple example#

You purchase a furnished studio in January 2026 and start renting it out on February 10, 2026. The February 10 rental start date is what drives the formality — not the date of purchase.

Being "non-professional" in the tax sense does not exempt you from administrative registration. LMNP does not mean "no registration required".

This confusion is common because the LMNP label sounds reassuring. But the status does not eliminate core obligations. In 2026, three levels need to be distinguished clearly:

• the existence of the activity;
• administrative identification via the SIRET;
• the choice of tax and reporting régime.

Many landlords also assume the SIRET is only relevant under the real régime. That is incorrect.

The practical rule is straightforward: the longer you wait, the more you risk your obligations lagging behind your first rental.

The right moment#

• before the property goes on the market, if you can plan ahead;
• at the latest within 15 days of the actual start date;
• as soon as your first furnished lease is signed and the activity begins.

If you own several properties or are building a rental strategy, it is better to record the correct start date from the outset. That avoids late corrections at the time of your annual income tax return.

The request goes through the formalities counter (guichet des formalités). The principle is to declare the start of your furnished rental activity and let the system assign an identifier.

Here is the process to follow:

1. identify the actual rental start date;
2. gather information about the property and yourself as landlord;
3. declare the start of activity online;
4. retrieve and keep your SIRET safely;
5. then link that SIRET to your tax obligations.

The most sensitive step is not the tool itself but the consistency of the information you enter. A wrong date or an incorrectly described activity type can create complications later.

What to have on hand#

• the address of the rental property;
• the actual rental start date;
• your full identity and contact details;
• civil-status or corporate information if the property is held through a company;
• your preferred tax régime if you have already decided.

The SIRET is often the entry point for the professional online space (espace professionnel). Depending on your situation, it may be needed for tracking tax notices, filing returns electronically or communicating with the administration.

That does not mean every LMNP landlord must use the same tools in the same way. But in practice, a clean and complete file avoids wasted time tracking down information later.

In 2026, the right approach is to build a coherent foundation from the start:

• SIRET obtained at the correct time;
• tax régime identified and recorded;
• tax address and property address properly aligned;
• possible future switch to the real régime anticipated;
• supporting documents archived in a simple, retrievable way.

Yes. The micro-BIC régime does not remove the registration requirement. The tax régime and the SIRET are two separate matters.

You can be:

• LMNP on micro-BIC with a SIRET;
• LMNP on the real régime with a SIRET;
• a landlord planning to transition from LMNP to LMP with the SIRET already in place.

The SIRET does not change your tax treatment on its own. It identifies your activity. The tax régime is what determines how income, expenses and depreciation are calculated and declared.

• starting to rent without declaring the start of activity;
• believing SIRET is only needed for LMP landlords;
• waiting for the first income tax return to sort things out.

There are also subtler errors:

• requesting the SIRET but not verifying the start-of-activity date entered;
• confusing the property's SIRET with a personal identifier;
• not linking the SIRET to the correct tax file;
• overlooking the downstream effects on CFE or the future annual tax package.

A practical example#

If you bought a flat in 2025 but only start renting it out in March 2026, the LMNP start-of-activity date must be the actual launch date. That is the date that counts for the formality and for the correct reading of your file going forward.

Hayot Expertise advice: in LMNP, a SIRET is not a comfort option. It is a core building block of your filing security.

Support becomes useful in three situations:

• you are starting out and want to get things right from day one;
• you have already been renting without clear registration formalities in place;
• you are switching to the real régime or moving to a more structured filing approach.

In practice, an accounting or tax adviser who truly understands LMNP helps you avoid the classic double trap: acting too late or acting incorrectly.

We help landlords carry out the right formalities from the start and properly align SIRET, tax régime, CFE and déclarations.

Quick link: Put your LMNP on solid administrative foundations

In 2026, an LMNP landlord should have a SIRET from the start of activity. The real question is not "do I need a SIRET?" but "did I complete the formality at the right time and with the right information?"

If you take away one idea, let it be this: the SIRET is not an optional formality. It is the entry point to your LMNP file, and it needs to be correct from the very start.

(Official sources: impôts.gouv.fr - start of furnished rental and professional space activity)