Indexation of a short-term lease in Belgium
Lease ≤ 3 years: indexation rules, calendar, automatic switch to 9-year lease, practical cases for student rentals and transitions.
Brief answer
In Belgium, a short-term lease (≤ 3 years, law of 20 February 1991) follows the same indexation rules as a 9-year lease: one annual indexation maximum at the anniversary date, official formula, mandatory written request. The specificity is arithmetic: a 1-year lease allows no indexation (term before the 1st anniversary date), a 2-year lease allows 1, a 3-year lease allows 2. Many landlords contractually waive indexation for the short duration (valid clause).
Typical case: 1-year student lease = no indexation possible. For this tenant over several years, sign a 3-year lease (2 indexations) or renew via successive leases with renegotiated rent at each renewal.
The short-term lease: legal framework
Defined by the law of 20 February 1991 (article 3 §6), the short-term lease is any principal residence lease:
- Of a duration explicitly written ≤ 3 years
- With a specific mention in the contract (failing which, automatic switch)
- Subject to the same registration obligations as the 9-year lease
Typical use cases:
- Student rental (1 year renewable)
- Rental for expatriate or executive on temporary mission (2-3 years)
- Transition rental between two life situations (separation, awaiting purchase, etc.)
- Test rental for the landlord who wants to evaluate a tenant before committing for 9 years
- Rental for professional in training (secondary residence, work-study student)
How many indexations possible according to duration
| Lease duration | Possible indexations | Calendar |
|---|---|---|
| 6 months | 0 | Term before 1st anniversary date |
| 10 months | 0 | Term before 1st anniversary date |
| 1 year | 0 | Term exactly at the 1st anniversary date (no effect) |
| 18 months | 1 | 1st anniversary date at 12 months → indexation 1 month later |
| 2 years | 1 | At the 1st anniversary date (12 months) |
| 30 months | 2 | At the 1st and the 2nd anniversary date (24 months) |
| 3 years | 2 | At the 1st and the 2nd anniversary date |
| 3 years + 1 day | switch to 9 years | See following section |
The exactly 1-year lease is ambiguous: the 1st anniversary date coincides with the term. Practice has it that no indexation is notified (the lease expires the same day), unless a renewal addendum is signed in advance, in which case indexation can apply for the following period.
Automatic switch to 9-year lease
This is the most important legal point of the short-term regime: two situations trigger an automatic switch:
Situation 1: total duration > 3 years
If the lease (with its possible written extensions) exceeds 3 cumulative years, it automatically switches to a 9-year principal residence lease. The original date remains that of the initial signature.
Consequence on indexation: opening of the 8 classic annual indexations (cf. our 9-year lease guide). The rent already indexed during the short phase is preserved as a new base.
Situation 2: no notice given at expiration
If at the end of the short lease, neither party has given notice within the legal deadlines (3 months before the term, by registered mail), the lease also switches to 9 years from the initial signature.
Practical consequence: a 3-year lease not denounced automatically becomes a 9-year lease, with 6 years of residual duration and 6 additional potential annual indexations. Many landlords « forget » to give notice and find themselves involuntarily committed for 6 more years.
The trap: if the landlord does not wish the switch, they must send a formal notice (registered mail) at least 3 months before the expiration of the short lease. Without this notice, the switch is automatic and legally irrevocable.
The indexation waiver clause: very widespread
To simplify management, many landlords include in the short lease an express waiver clause of indexation:
« The parties expressly agree that the monthly rent will remain fixed at [X] € for the entire duration of this short-term lease, to the exclusion of any indexation within the meaning of article 1728bis of the Civil Code. »
This clause is legally valid as long as the lease remains short-term. It presents several advantages:
- Administrative simplicity: no notification to send
- Readability for the tenant: predictable amount until term
- Commercial argument: « no surprise on the rent »
If the lease switches to 9 years (cf. supra), the waiver clause automatically falls and indexation becomes possible again at future anniversary dates.
Worked examples by duration
Case A: 1-year student lease
- Rent: 600 €/month fixed
- Duration: 12 months (Sept 2025 → Sept 2026)
- Indexations: 0 (no effective 1st anniversary date)
- Total rent collected: 600 € × 12 = 7,200 €
Case B: 2-year expatriate lease
- Initial rent: 1,200 €/month (signed Sept 2024)
- 1st possible indexation Sept 2025 (~+30 €/month) → rent 1,230 €/month
- Duration: 24 months
- Indexations: 1
- Total rent collected: (1,200 × 12) + (1,230 × 12) = 29,160 € (vs 28,800 € without indexation)
Case C: 3-year transition lease
- Initial rent: 900 €/month (signed Jan 2024)
- 1st indexation Jan 2025 → ~+25 €/month
- 2nd indexation Jan 2026 → ~+30 €/month
- Duration: 36 months
- Indexations: 2
- Total rent collected: (900 × 12) + (925 × 12) + (955 × 12) = 33,360 € (vs 32,400 € without indexation)
Case D: short lease with automatic switch
- Lease signed for 3 years in June 2023
- No notice given in March 2026
- → Switch to 9-year lease retroactively to June 2023, term June 2032
- 2 indexations already applied (June 2024, June 2025) + 6 future possible indexations (June 2026 → June 2031)
To calculate your exact case, use the calculator.
Procedure to notify an indexation on a short lease
Identical to a 9-year lease:
- Verify registration of the short lease (obligation 2 months post-signature)
- Verify the absence of waiver clause in the contract (otherwise, indexation contractually excluded)
- Calculate via the calculator by entering the signature date and the anniversary date
- Notify by registered mail (cf. our registered mail guide) 1 to 2 months before the anniversary date
- Follow up the adjustment of the tenant’s standing order
Special cases to know
Seasonal lease (short rental of 2-3 months)
Different legal regime: this is not a residential lease but a temporary use rental (often rented for holidays, training, event). Article 1728bis does not apply. No mandatory registration, no indexation possible — the rent is fixed contractually and stable for the duration.
Replacement lease (authorised sublease)
If the main lease authorises subletting, the sub-tenant remains bound to the sub-landlord (the main tenant). Indexation between sub-landlord and sub-tenant is possible according to the same rules, but it cannot exceed the indexation applied by the owner to the main tenant.
Concurrent lease with tenant change
If the main tenant gives notice during the short lease, the landlord can sign a new short lease with another tenant (renegotiable rent, no inheritance of the indexation history). It is a complete reset.
Lease assignment (rare in short lease)
If the assignment is authorised, the new tenant takes over the lease as is: same residual duration, same rent (including already applied indexations), same clauses (including possible indexation waiver).
Frequent errors on short-term leases
| Error | Consequence |
|---|---|
| Notify an indexation on a 1-year lease | Without effect (no 1st anniversary date) |
| Forget to give notice at the expiration of a short lease | Automatic switch to 9-year lease |
| Notify without taking into account a waiver clause | Contestable indexation, tenant can refuse |
| Count the short lease as « non-registrable » | False, registration remains mandatory |
| Believe that the 3rd year allows a 3rd indexation | The 3rd date is the term, not an indexation |
| Confuse seasonal lease (holidays) and short residential lease | Distinct legal regimes |
| Renew verbally without addendum | Automatic switch to 9 years beyond 3 years |
To go further
- 9-year lease and indexation — common law regime
- When can one index a rent? — temporal rules
- How to calculate an indexation — step-by-step method
- Indexation and co-tenancy — special regime
- Unregistered lease — sanction common to both regimes
- Calculate my indexation — official tool
- Notification template — adaptable form letter
- The law on indexation — detailed legal sources
- Methodology — calculation sources
The short lease has its own logic: few indexations, automatic switch to monitor and very widespread waiver clause. Reading the contract carefully before any notification is the basic rule.
Frequently asked questions
Can a 1-year, 2-year or 3-year lease be indexed? + −
Yes. The annual indexation rule (article 1728bis of the Civil Code) applies to all registered residential leases in Belgium, whatever their duration. For a 1-year lease, no indexation possible (the lease expires before the 1st anniversary date). For a 2-year lease, 1 indexation possible at the 1st anniversary date. For a 3-year lease, 2 indexations possible (1st and 2nd anniversaries). The 3rd date marks the term.
Does the short-term lease automatically switch to a 9-year lease? + −
Yes, in two cases: 1) if the total duration of the lease (including renewals) exceeds 3 years, or 2) if at expiration neither party has given notice within the legal deadlines (3-month notice). The switch transforms the short-term lease into a 9-year principal residence lease from the origin, which then opens the 8 classic annual indexations. Important: the indexed rent already applied during the short phase is preserved.
Many landlords include a fixed rent for 1-2 years. Is this legal? + −
Yes, the landlord can contractually waive indexation for the duration of a short-term lease (express clause in the contract). This waiver is valid as long as the lease remains short-term. If the lease switches to 9 years, the waiver clause falls and indexation becomes possible again at future anniversary dates. This practice is very widespread in student or expatriate leases where simplicity prevails over financial optimisation.
For a 10-month student rental, can one index? + −
No, never. A 10-month rental does not reach the 1st anniversary date (12 months). Indexation supposes at minimum having crossed a complete lease year. For a regular landlord-student relationship (year-by-year renewal), one would have to either sign a 2-3 year lease with indexation at each anniversary, or sign a new lease each year with a renegotiated rent.
Does a registered short-term lease give the same rights as a 9-year lease? + −
Yes, from the indexation point of view. Registration remains mandatory within 2 months of signature, and conditions the exercise of the right to index (without registration, no indexation possible). Our unregistered lease guide details the consequences. From the point of view of other rights (notice, termination grounds, rental guarantee), the regimes differ — see the Civil Code and the law of 20 February 1991.
Can a short lease be transformed into a 9-year lease midway? + −
Yes, by addendum signed by mutual agreement. The transformation takes effect on the date of the addendum and opens annual indexations from the next anniversary date. The reference rent for the calculation remains that of the original signature of the short lease. This manoeuvre is useful when landlord and tenant find that the relationship is lasting beyond 3 years: avoiding the automatic switch avoids uncertainty.
Calculate your indexation
Our tool automatically applies the Belgian legal formula with up-to-date Statbel indexes.
Go to the calculator →This article is informational and does not constitute legal advice. For any disputed or complex situation, consult a lawyer or the justice of the peace of the property's commune (free procedure).