Falling due requires two things
The fee falls due once the work has been accepted and a verifiable final fee account has been handed to the client. Both conditions must be met, and the second lies entirely in the designer's hands.
Falling due is the precondition for a legally enforceable claim to payment. Without it neither the obligation to pay nor default begins.
Whether the verifiability requirement applies with equal rigour to interim accounts is contested. To avoid uncertainty, preparing interim accounts with the same care as the final account is advisable.
What the account must contain
Verifiability requires that the client can follow the account without conducting enquiries of their own. The necessary entries follow from that.
| Entry | Why it is required |
|---|---|
| Chargeable costs | the fee basis, with derivation from the cost calculation |
| Fee zone | determines the applicable band, with reasons |
| Fee rate | the position chosen within the band |
| Work phases with percentages | the share invoiced |
| Weighting of incomplete phases | on partial commissions or early termination |
| Supplements | conversion supplement, increase for repair work |
| Additional services | shown separately, with their agreement |
| Ancillary expenses | lump sum or on individual evidence |
| Interim payments | deducted, with date and amount |
| Value added tax | on the total |
The third and fifth rows are where accounts most often fail. Both concern quantities the ordinance no longer sets itself.
The fee rate must be stated. It has been freely negotiable since 2021, but for that very reason the account must show which rate underlies it and what it rests on.
The weighting of incomplete phases must be disclosed. Where not all basic services of a phase were commissioned or performed, for instance after early termination, the parts performed must be shown and weighted as percentages. Since the HOAI does not weight individual basic services, assessment tables from the professional literature are used. The source relied upon belongs in the account.
The client's obligation
Verifiability is not a one-way street. A client considering an account unverifiable must object and state concretely why they cannot follow it.
A blanket assertion of unverifiability does not suffice. The client must identify which entry is missing or which step they cannot follow.
A practical note follows for the designer: a blanket objection is worth answering with a request for the specific entry said to be missing. It frequently emerges that the account is verifiable and the objection serves another purpose.
Verifiability must also be distinguished from correctness. A verifiable account may be substantively wrong; it then falls due but is assailable as to amount. An unverifiable account does not fall due, regardless of whether it is substantively right.
What dates from the era of price law
A substantial part of the case law and literature on verifiability arose under binding price law. A distinction is needed when applying it.
| Part of the received requirements | Status |
|---|---|
| The account must be capable of being followed | unchanged |
| The due date depends on it | unchanged |
| The client must object concretely | unchanged |
| That the fee zone cannot be freely agreed | to be examined, attaches to the binding nature of the rates |
| That a dispute over the zone automatically corrects the fee | out of date where a valid agreement on the level exists |
What must be examined is everything attaching to the binding nature of the rates. Statements such as the one that the fee zone cannot be freely agreed carried a concrete meaning under the old law: the zone determined the mandatory minimum rate, and a divergent agreement would have undercut it.
Since the level became freely negotiable, the function has shifted. The zone remains an objective quantity to be determined from the assessment criteria, but its significance today lies in deriving the fee agreed rather than in setting a floor.
For the account this means: the zone should still be stated and justified, because it carries the derivation. A dispute about its correctness no longer automatically corrects the fee, however, where a valid agreement on the level exists.
Structure in practice
A structure in five sections works well, allowing the check to proceed in the same order as the calculation. The reviewer can then follow the arithmetic step by step rather than hunting for entries.
- Contractual basis. Contract date, phases commissioned, agreed fee rate, reference to the fee agreement.
- Fee basis. Chargeable costs with derivation, existing fabric where applicable, fee zone with reasons.
- Base fee. Table value, interpolation where needed, percentages of the phases invoiced, subtotal.
- Supplements and further items. Conversion supplement, additional services, ancillary expenses.
- Settlement. Interim payments, value added tax, final sum.
The second section is the one most often too brief. A reference to the cost calculation does not suffice where the client does not hold it in the same structure. The system of comparability is covered in the article on target-actual comparison.
The link to the editions of DIN 276
One point bears directly on verifiability. For determining chargeable costs the HOAI refers to the December 2008 edition of DIN 276, while cost planning itself proceeds under the 2018 edition.
Where the account rests on a cost structure the client cannot follow, or one not corresponding to the governing edition, they may reject it as unverifiable. A documented reconciliation between the two structures is therefore not merely professionally sound but the most effective protection against that objection.
The system is covered in the article on the version problem. It also sets out which cost groups moved between the two editions.
Related articles
This article reflects the position of the rules and case law at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.