SolutionsLeases and indexation
Rent that rises on time.
With the arithmetic attached.
Indexation is money already written into your lease, and across most of Europe it lapses if you do not claim it on the date. Dardaris watches every anniversary, calculates the new rent the way your region calculates it, and hands you the letter with the working inside it.
Dardaris is early and still moving. Nothing is switched on until you say so.
Indexation, Flanders
Anniversary 1 Sep 2026
€951.59 from €900.00
+€51.59 a month, €619.08 across the year
- Base rent, excluding charges€900.00
- ×Health index, August 2026132.80
- ÷Health index, August 2019125.60
Nothing is owed in Belgium until a dated written demand goes out. Dardaris writes it, with this arithmetic inside it.
Next three anniversaries
- Kortrijksesteenweg 88, 2A1 Sep 2026, now €900.00Letter drafted
- Zandstraat 41 Nov 2026, now €1,340.00Index due 30 Oct
- Dokkaai 12, 1F1 Dec 2026, now €1,090.00Confirm the PEB
What today costs
A missed anniversary is not deferred. It is gone.
Belgium indexes the original rent, so next year the level comes out right again. The twelve months you did not charge for in between are simply never charged.
The anniversary that went past in March
A demand written in December reaches back to 1 October and no further. Nine months of the increase does not roll into next year, it is money that will never be invoiced.
Two index values on different base years
A 2013 = 100 figure divided by a 2004 = 100 one produces a plausible-looking rent that is wildly wrong. It is the error that gets a whole increase contested rather than argued down.
The lease still sitting unregistered
Registration is free and due within two months of signature. Without it a Belgian tenant on a nine-year lease can walk out with no notice and no indemnity, and in Brussels and Wallonia the indexation you claimed on it is invalid too.
How it works
It watches the date, does the arithmetic, then waits for you.
The division is not the hard part. Doing it on the right day, from the right base rent, on two index values published on the same base year, across a portfolio where every anniversary falls somewhere different, is what actually goes wrong.
- Step 1
The lease is read into a shape
Region, type, start date, base rent excluding charges, the base index month, and whether the lease carries an indexation clause at all. No clause, no increase.
- Step 2
The anniversary is watched
Dardaris knows the date, and knows the index it needs is published near the end of the month before. It waits for the published figure instead of estimating one.
- Step 3
The rent is calculated, with the working
Base rent, both index values with the month each came from, any correction factor, and the result. The same sentences go straight into the letter.
- Step 4
The demand waits for your signature
Drafted, dated, and carrying the day it has to be sent by to keep the full amount. Nothing leaves until you say so.
The window closes, and the money does not come back
An indexation you forget is not carried into next year. Belgium lets a demand reach three months back, France forfeits the whole year at twelve months, and the Netherlands allows nothing at all. This is the calendar Dardaris watches, one lease at a time.
Belgium
0 to 3 monthsFull amount3 to 12 monthsA month lost for every month you wait€464 gone
A dated written demand reaches back to the three months before the month you send it, and no further. Flanders, Brussels and Wallonia all read it that way.
France
0 to 12 monthsFull amountafter 12Forfeited€619 gone
The revision has to be claimed within twelve months of the revision date. The day after that, the whole year is forfeited outright.
Netherlands
from the noticeChargedanything earlierNever recoverable€619 gone
There is no back-claiming at all. An increase runs from the date written on the notice and not one day before it.
Gone is what a year of silence costs on the €900 lease above, at €51.59 a month.
Six jurisdiction packs, and Belgium is three of them. Flanders, Brussels and Wallonia have run separate lease regimes since 2018 and 2019, and the region is decided by where the building is, never by where you live.
What you get
The whole lease file, from the first clause to the deposit coming back.
A lease assembled from clauses, not a template you overwrite
14 contract types and a library of 36 drafted clauses, each carrying its text in Dutch, French, English and German. Every clause knows the regions that require it and the regions that render it void, and the document renumbers itself when one comes out.
Woninghuurovereenkomst, 9 jaar
36 clauses in the library
- Art. 5Duration and entry into force
- Art. 7Annual indexation of the rentHealth index
- Art. 9Rental deposit3 months here
- Art. 12Late paymentVoid in France
- Art. 22Termination by the LandlordVoid in the Netherlands
Indexation, with the correction your region applies
The health index in Belgium, the IRL in France, a statutory percentage cap per sector in the Netherlands. A poor energy label cuts the increase in Brussels and Wallonia and blocks the revision outright in France.
Same lease, PEB E, Wallonia
€900.00 + (€951.59 − €900.00) × 0.50
A poor energy label got half the increase, and that restricted figure became the permanent base rent. Apply it where it does not belong and you overcharge forever.
Registration tracked against its deadline
A Belgian residential lease goes to the tax authority within two months of signature, online only since March 2025 and free. Dardaris files it, keeps the proof, and escalates daily once the window narrows.
Lease registration
Filed on day 8Two months from signature, online only, and free of charge.
Notice and renewal, counted back from the date
Three months for a tenant on a Flemish nine-year lease, six for the landlord and only on a permitted ground. The early exit indemnity falls from three months of rent to two, then one, then nothing. Dardaris counts back and tells you when each window opens.
Deposits held the way your region requires
Three months in Flanders, two in Brussels and the Netherlands, one on an unfurnished French lease. In Belgium a blocked account in the tenant’s name or a bank guarantee, with the interest belonging to the tenant, and no deduction proposed where there is no entry inventory to compare it against.
Where it stops
It never sends a rent increase you have not read.
It calculates the increase. Sending it is your signature.
Indexation sits at Review by default and never goes out unseen. Dardaris does the arithmetic, writes the demand with the working in it, and parks it on your desk together with the date it has to be sent by. It does not give legal advice, and where a rule could not be confirmed against a primary source it says so on the figure rather than presenting it as fact.
Waits for you, every time
- The indexation demand, every single time
- Any figure resting on a rule marked confirm this
- Notice to end a tenancy, and the terms of a renewal
- A deduction from a deposit, or a deposit released early
Everything else it does, and writes down why.
Hand over this part first.
Bring one building. Watch a month of it running. Move the rest across only if the month convinced you.
Nothing to move first · Nothing switched on until you say so
The rest of the job