In August 2026, the health index reached 103.49 in base 2025, or 140.30 in base 2013, up 3.44% year on year. For leases whose anniversary falls this autumn, indexation will therefore be higher than in 2025. Here are the known indices, the Federal Planning Bureau’s forecasts for the following months, and the method for handling the October to December anniversaries in batches.

Which indices are known on 2 September 2026?

On 28 August 2026, Statbel published the August price index. The health index rose by 0.25 points in August to 103.49, against 103.24 in July. Since January 2026, Statbel has published the index with the reference year 2025 = 100. The older bases remain available in its table by base year.

Month Health index, base 2025 Health index, base 2013
June 2026 102.59 139.08
July 2026 103.24 139.96
August 2026 103.49 140.30

For rents, the health index is what counts, not general inflation. It excludes alcoholic beverages, tobacco and fuels, except LPG. Year on year, its increase rose from 2.99% in June to 3.22% in July, then to 3.44% in August. General inflation reached 3.97% in August, driven by energy (+16.47%), including gas (+24.9%) and motor fuels (+24.1%). The gap between the two figures comes partly from motor fuels, which the health index leaves out. For an agency, the consequence is concrete. A lease whose anniversary falls in September, indexed in 2025 and again in 2026, sees its rent rise by 3.44%: that is the increase in the health index between August 2025 and August 2026. Statbel also notes that rents themselves, as measured in the price index, rose by 3.11% year on year. These figures let the agency tell owners the order of magnitude of the autumn indexations before running the calculations lease by lease.

What does the Federal Planning Bureau forecast for the autumn?

On 1 September 2026, the Federal Planning Bureau published its inflation forecasts. It expects the health index to grow by 3.2% on average in 2026 and 3.4% in 2027. For comparison, this growth was 3.28% in 2024 and 2.63% in 2025. General inflation would reach 3.6% on average in 2026 and 3.4% in 2027. The Bureau also expects the next pivot indices, 102.29 and 104.34 in base 2025, to be exceeded in December 2026 and July 2027. These thresholds trigger the indexation of social benefits and public sector salaries, not of rents. For an agency, the useful forecast is the monthly one. It shows that the October to December anniversaries will fall on higher indices than August’s, and roughly by how much. The Bureau will publish its next update on 6 October 2026. Its monthly health index forecasts, in base 2025, are as follows:

Month Forecast health index (base 2025)
September 2026 103.93
October 2026 104.64
November 2026 105.28
December 2026 105.55

These are forecasts, not indices. Indexation is always calculated on the index published by Statbel, never on a forecast. Their use lies elsewhere: warning owners of the order of magnitude, and preparing letters before the index is published.

Which index applies to each autumn anniversary?

The new index is that of the month preceding the anniversary of the lease’s entry into force. A lease whose anniversary falls in September therefore uses the August index, published on 28 August: 103.49 in base 2025. For an October anniversary, the September index is needed, which Statbel publishes at the end of the month. For November, the October index; for December, the November index. Base 2025 does not change the method rule: the new index and the starting index must be expressed in the same base. Statbel stresses that values with the same base year must absolutely be used. A lease signed in 2019, whose starting index was published in base 2013, is calculated with the August index in base 2013, namely 140.30. The same calculation in base 2025 gives the same rent, provided the starting index is also converted. For an agency, the mistake to avoid is mixing both bases in a single calculation.

The detailed calculation, with each region’s rules, is in our guide to calculating rent indexation. For older leases, see also indexation in base 88.

Which correction factors apply from October to December?

In Flanders and Brussels, some leases concluded before autumn 2022 are still subject to a correction factor linked to the energy certificate. In Flanders, it covers leases that entered into force before 1 October 2022, with label D, E, F or no EPC. In Brussels, it covers leases that entered into force before 14 October 2022, with EPC E, F or G. The factor is multiplied by the result of the standard formula, and it depends on the anniversary month:

Anniversary Flanders, label D Flanders, E, F or no EPC Brussels, EPC E Brussels, EPC F or G
1 to 13 October 0.949447646 0.898895293 0.989805521 0.979611041
14 to 31 October 0.949447646 0.898895293 0.949447646 0.898895293
November 0.945356473 0.890712946 0.945356473 0.890712946
December 0.951977401 0.903954802 0.951977401 0.903954802

These values come from the official Flemish page; the Brussels Region publishes its own for classes E and F-G: identical to the Flemish values, except for anniversaries from 1 to 13 October. In Flanders, the factor applies at every indexation, until a better EPC or a new lease. In Wallonia, leases affected by the 2022-2023 limitation keep a specific calculation method until the end of the lease.

How should the autumn anniversaries be handled in batches?

For an agency, autumn 2026 is not a question of formula but of volume. Each month brings its batch of anniversaries, with different regions, bases and sometimes factors. The method has six steps:

  1. List next month’s anniversaries, with the region, the date of conclusion and the date of entry into force.
  2. Check the conditions in batches: written lease, no clause excluding indexation, registration in Brussels and Wallonia, EPC provided in Brussels.
  3. Identify leases with a correction factor: entry into force before autumn 2022 and a relevant energy label.
  4. Calculate in a consistent base, as soon as the previous month’s index is published.
  5. Send the written request in the anniversary month: retroactive effect is limited to the three months preceding the request.
  6. Archive the letter and the calculation on the lease record, to answer any dispute.

On 31 August 2026, Federia made an indexed rent calculator available to its members, developed with the law firm DECODE. It takes into account the region, the rent and the lease dates, and the EPC. The Statbel rent calculator remains open to all.

For commercial leases, which are not subject to EPC limitations, see our article on overpaid indexation under a commercial lease.

How does Seido help index a whole portfolio?

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

Can an October rent be indexed using the Planning Bureau’s forecast?

No. The statutory formula uses the health index of the month preceding the anniversary, as published by Statbel. For an October 2026 anniversary, that is the September index, published at the end of September. The Planning Bureau’s forecast (103.93 in base 2025) only helps anticipate the order of magnitude and warn owners. A letter calculated on a forecast would have to be corrected if the published index differs.

Does base 2025 change the amount of the indexed rent?

No, if the calculation is consistent. According to Statbel, the change of reference year has no impact on measured inflation. The new index and the starting index simply need to be expressed in the same base, whether 2013 or 2025. The mistake to avoid is mixing the two: dividing an index in base 2025 by a starting index in base 2013 would give an indexed rent far below the correct amount.

Must the indexation request be sent before the anniversary?

It is not necessary, but it should not be delayed. Indexation is not automatic for a residential lease: the landlord must request it in writing. If the request comes later, the retroactive effect is limited to the three months preceding the month of the request. For a portfolio, sending the letters in the anniversary month avoids any loss.

Does exceeding the pivot index affect rents?

No. The Planning Bureau expects the pivot index of 102.29 to be exceeded in December 2026, which triggers the indexation of social benefits and public sector salaries. Rents follow a different rule: they are indexed once a year, on the lease anniversary, using the previous month’s health index, with no link to the pivot index.

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.