On the anniversary of the lease, the landlord may index the rent using a statutory formula, on written request. But the formula is not enough: in all three regions, a poor EPC still reduces indexation for many leases concluded before autumn 2022. Here are the rules in force, region by region, and the change of base of the health index in 2026.

What is rent indexation?

Indexation adjusts the rent to changes in the cost of living, measured by the health index that Statbel publishes every month. It is not a free increase: it is an adjustment capped by a statutory formula.

The basic conditions are similar in all three regions:

  • The lease is in writing. An oral lease cannot be indexed.
  • The lease does not exclude indexation through an express clause.
  • The landlord requests indexation in writing: for a residential lease, it is never automatic.
  • The request has retroactive effect only for the three months preceding the month of the request.

Regional conditions come on top, in particular lease registration and the EPC, described below.

What is the calculation formula?

The formula is the same in all three regions:

New rent = Base rent × (New index / Starting index)

Base rent: the rent resulting from the lease or from a judgment, excluding costs and charges.

New index: the health index of the month preceding the anniversary of the lease’s entry into force.

Starting index: the health index of a reference month that depends on the region (see below).

The result is a ceiling: the indexed rent may not exceed it. Systematically rounding up therefore means exceeding the legal maximum.

What does the 2025 base of the health index change?

Since 29 January 2026, Statbel has published the price index with the reference year 2025 = 100. The change does not alter measured inflation, but it changes the scale of the figures. In August 2026, the health index stands at 103.49 in base 2025 and 140.30 in base 2013. Yet most current leases have a starting index published in an earlier base. The method rule is simple: the new index and the starting index must be expressed in the same base. Dividing an index in base 2025 by a starting index in base 2013 would produce an indexed rent far below the correct amount. Statbel still publishes the older bases in its “Health index by base year” table: June, July and August 2026 stand at 139.08, 139.96 and 140.30 in base 2013. The Statbel rent calculator makes this choice of base automatically.

For older leases whose starting index predates 2013, our article on indexation in base 88 explains the same logic. For the autumn 2026 indices and the Planning Bureau’s forecasts, see our article on autumn 2026 rent indexation.

Which starting index applies in your region?

Brussels and Wallonia

The starting index is the health index of the month preceding the conclusion of the lease, in other words its signature. Example: a lease signed on 15 March 2020 has February 2020 as its starting index. The rule appears in the official Brussels information and in Article 26 of the Walloon Decree of 15 March 2018.

Flanders

The Flemish Residential Lease Decree, which applies to leases concluded since 1 January 2019, uses the index of the month preceding the lease’s entry into force, not its signature. The difference matters when signature and move-in are several months apart.

How does the EPC still limit indexation?

During the energy crisis, the three regions limited indexation for energy-inefficient homes. These temporary measures ended in 2023, but each left a lasting effect on leases concluded before autumn 2022.

Brussels: a correction factor for EPC E, F and G

Until 13 October 2023, indexation of high energy consumption homes was restricted. Since 14 October 2023, it has been allowed again, but with an adapted formula. According to the official Region page, the landlord must apply a correction factor if three conditions are met. The lease entered into force before 14 October 2022. The EPC is E, F or G. The home is let on the private or public market, excluding homes of the SISP and the Fonds du Logement. The factor depends on the anniversary month and the certificate: for a November anniversary, it is 0.945356473 for EPC E and 0.890712946 for EPC F or G. It is multiplied by the result of the standard formula. Homes rated A to D are indexed without correction.

Wallonia: a 2022-2023 limitation that still shapes the calculation

From 1 November 2022 to 31 October 2023, Walloon indexation was limited according to the EPC. It remained full for classes A, B and C. For EPC D, only 75% of the indexation amount could be requested; for EPC E, 50%. No indexation was possible for EPC F or G, or without a certificate. The measure was not renewed, but it leaves a specific calculation method for homes rated D, E, F or G and those without a certificate. The base rent becomes the rent adjusted during that period. The starting index becomes that of the month preceding the anniversary that fell within that period. This calculation applies until the end of the lease. Leases that started after 31 October 2022 are not affected.

Flanders: a correction factor for labels D, E, F and no EPC

In Flanders, an adapted formula applies if the lease entered into force before 1 October 2022 and the home has label D, E or F, or no EPC. An expired EPC counts as no EPC. The landlord multiplies the result of the standard formula by a correction factor published for each anniversary month. For a November anniversary, it is 0.945356473 for label D and 0.890712946 for label E, F or no EPC. Label D has therefore not returned to full indexation. The factor applies at every indexation, until a better EPC is available or a new lease starts. Only labels A+, A, B and C allow full indexation.

Which special cases should you know?

Commercial leases

Commercial leases remain governed by Article 1728bis of the former Civil Code. The EPC-related limitations described above concern homes, not commercial leases. The same formula applies, with the index of the month preceding the conclusion of the lease as starting index. Our article on overpaid indexation under a commercial lease covers recovering amounts wrongly collected.

Unregistered leases

  • Wallonia: to index a main residence lease since 1 September 2018, the lease must be registered.
  • Brussels: the landlord must have registered the lease and given the tenant a valid EPC.
  • Flanders: the Residential Lease Decree does not make registration a condition for indexation. The EPC label, however, may require the correction factor.

Retroactivity

A landlord who forgot to index for several years only recovers the three months preceding the month of the written request. For earlier years the right is lost, but the indexed rent can be requested for the future.

How do you index a whole portfolio without errors?

For an agency, the issue is not a single calculation but a series of deadlines. Each lease has its anniversary month, its region, its index base and sometimes its correction factor. A wrong base or a forgotten factor is then repeated at every anniversary. The method has four steps. List next month’s anniversaries. Check registration and the EPC in batches. Calculate in a consistent base. Then send and archive each written request.

Managing several properties? Seido alerts you at each anniversary date, prepares the indexation letter and tracks leases and EPCs. You approve each proposal before it is sent. See how Seido handles indexation and deadlines under the Belgian framework.

Frequently asked questions

Is indexation mandatory?

No. Indexation is a right of the landlord, not an obligation. It is not automatic for a residential lease: the landlord must request it in writing from the tenant. As long as they do not, the rent stays the same. If the request comes late, the retroactive effect is limited to the three months preceding the month of the request. For an agency, this is why every anniversary date should be tracked rather than indexing as things come up.

Should you start from last year’s rent or the initial rent?

From the base rent, meaning the rent resulting from the lease or from a judgment. The formula is never applied in cascade to the previous year’s indexed rent. The ratio between the new index and the starting index already captures the whole change since the start of the lease. Walloon exception: for homes affected by the 2022-2023 limitation, the base rent becomes the rent adjusted during that period.

What happens if the EPC improves after works?

In Flanders, the correction factor stops applying as soon as a better EPC is available, according to the official page. A home that moves to label C or better therefore returns to full indexation. In Brussels, the factor targets homes with an E, F or G certificate: a D certificate or better takes the home out of the mechanism. In both cases, keep the new certificate with the indexation request.

Does indexation apply to service charges?

No. The base rent excludes the costs and charges placed on the tenant by the lease, as the regional texts specify. Charge advances are adjusted according to actual expenses and the lease terms, and a flat-rate charge follows its own revision rules. Mixing rent and charges in the formula means indexing amounts that cannot be indexed.

Which index should you use: health index or consumer price index?

The health index. It is the consumer price index from which Statbel removes alcoholic beverages, tobacco and fuels, except LPG. It should not be confused with the smoothed health index, which Statbel publishes separately. In August 2026, the health index stands at 103.49 in base 2025, and its year-on-year increase is 3.44%.

Sources and references

Last updated: September 2026. This article is provided for information purposes only and does not constitute legal advice. For any specific situation, consult a real estate law professional.