Belgian Rent Indexation Calculator

The indexation formula

A Belgian residential lease can be indexed once a year, on the anniversary of its entry into force, if the landlord asks for it in writing. The formula is the same in all regions:

new rent = base rent × new index ÷ initial index

Both indices are Statbel health indices (gezondheidsindex / indice santé). The new index is that of the month before the anniversary. The initial index depends on the contract: for a Flemish main-residence lease concluded from 1 January 2019 it is the index of the month before the lease took effect; otherwise it is the index of the month before the lease was signed. The calculator picks both months from the dates you enter and fills in the official values.

Worked examples (base 2025 = 100)

Flanders, main residence, base rent € 950.00
  signed 2025-08-20, in force 2025-09-01, anniversary 2026-09-01
  initial index  2025-08  100.05
  new index      2026-08  103.49
  950.00 × 103.49 ÷ 100.05 = € 982.66   (+ € 32.66, +3.44%)

Brussels, main residence, base rent € 950.00
  signed 2025-09-15, in force 2025-10-01, anniversary 2026-10-01
  initial index  2025-08  100.05   (month before signature)
  new index      2026-09  103.76
  950.00 × 103.76 ÷ 100.05 = € 985.23   (+ € 35.23, +3.71%)

Rules and edge cases

Same base year. Statbel rebases the index (most recently to 2025 = 100). Both indices must come from the same base; the calculator refuses a mixed-base calculation when you enter values manually.
Older months. Recent months are bundled. If a required month is older, enter both indices yourself from the Statbel table on one base.
Base rent is the rent in the contract, without charges; a later legal rent revision replaces it.
No retroactivity beyond limits. The landlord must ask in writing; regional rules limit how far back an indexation can be claimed.
Energy-performance limits. Temporary EPC/PEB correction rules (2022-2023) in each region can still affect the amount; the official Statbel calculator covers them.
Leases signed before 1 February 1994 follow older regimes and are out of scope.

For wages and benefits use the indexation calculator; for deadlines use the working days calculator; for late rent the legal interest calculator.

Frequently asked questions

How is rent indexed in Belgium?

New rent equals base rent times the new health index divided by the initial health index. The new index is the one of the month before the anniversary of the lease.

Which initial index applies in Flanders?

For a Flemish main-residence lease concluded from 1 January 2019, the initial index is the health index of the month before the lease took effect. Otherwise it is the month before signature.

Can I mix indices on different base years?

No. Both indices must use the same Statbel base year. The calculator uses base 2025 = 100 and refuses manual values that are not entered as a pair.

Is indexation automatic?

No. The landlord must ask for it in writing. Without a request, the rent stays the same, and regional rules limit how far back it can be claimed.

Does the calculator include the EPC/PEB limits?

No. The temporary energy-performance correction rules are not applied. Compare with the official Statbel rent calculator when those rules may apply to your lease.