Checking interim payment applications: invoice, BoQ, measurement

Anyone who checks an interim payment application (Abschlagsrechnung) puts three documents side by side: the invoice with its statement of work, the bill of quantities (BoQ) with the contract prices, and the measurement that supports the quantities carried out. A fixed program recalculates quantities, prices, totals and previous payments. The AI prepares a deviation list with source references. What is accepted and paid is determined by the checker.

What the check covers

The contractor can demand an interim payment equal to the value of the work carried out and owed under the contract. If the work is not in conformity with the contract, the client may refuse an appropriate part of the payment. The burden of proof for conformity stays with the contractor until acceptance. In addition, the work must be proven by a statement that allows a quick and reliable assessment (all section 632a(1) of the German Civil Code, BGB).

The VOB/B (German standard contract terms for construction works), where agreed, puts it similarly: interim payments are granted at the value of the contractually compliant work proven in each case, including the VAT shown, and the statement must be “verifiable” (section 16(1) no. 1 VOB/B). The 2016 edition is cited here. According to the entry at DIN Media (DIN 1961:2016-09), it is still the current edition in November 2026. The official 2016 notice contains only the amendments to sections 4, 5 and 8. Sections 14 and 16 date from earlier notices. The citations therefore follow the unofficial reading version published by the Federal Ministry for Housing, Urban Development and Building. Three things are therefore checked: whether the work is owed under the contract, whether it was carried out, and whether it is valued correctly.

In site supervision this belongs to the basic services of phase 8 under Annex 10 of the HOAI (the German fee scale for architects and engineers). These include checking invoices and the measurements, joint measurement with the contractors, comparing the check results with the contract sums including variations, and cost control against the contract prices. In client-side project management the aim is that everything is plausible and correct, so that the client gets a consistent basis for decision. Who owes which check in your project is stated in the respective contract.

What lies side by side

Document	What you need from it
Interim payment application with statement	Items, quantities invoiced, unit rates, totals, VAT, interim payments already made
Bill of quantities	Item numbers, contract quantities, contract prices, item texts
Measurement, quantity calculations, evidence	Quantities carried out with sheet and line, drawings, delivery notes
Variations and payment status	Variations ordered, earlier interim payments, retentions, securities

Under section 14(1) VOB/B, quantity calculations, drawings and other evidence are to be attached to the invoice. Changes and additions to the contract must be marked clearly in the invoice. The findings needed for invoicing are to be made jointly where possible, in step with the progress of the work (section 14(2) VOB/B).

The arithmetical comparison in a fixed program

A program that you can follow should do the calculating, for example a spreadsheet with open formulas. The language model does not calculate. For each item and for the whole invoice, the program checks:

• The quantity invoiced against the measured quantity, and the total of all quantities so far against the contract quantity, with the deviation in per cent.
• The unit rate against the contract price, and quantity times unit rate against the item total.
• Variation items separately from contract items, each with a reference to the instruction.
• Item totals, VAT and the deduction of interim payments already made, down to the amount demanded, together with retentions and counterclaims.
• The total of all interim payments against the contract sum plus variations ordered.

Figures that the program has not confirmed carry the note “unchecked”. A figure that the AI has read from a measurement sheet enters the program’s calculation only once someone has compared it with the sheet.

The deviation list with source references

The AI reads the invoice, the bill of quantities and the measurement sheets. It matches each invoice item to the contract item and the measurement line and enters the source reference: document, sheet and line. Scanned measurement sheets must first be made readable by text recognition (see Old plans and poor scans). For every deviation the AI words a query. As with any AI answer, no source reference means no statement (see AI answers with a source reference).

An example with invented data: in the invoice, item 03.02.0040 shows a cumulative quantity of 412 m³. The measurement, sheet 7, line 12, shows 398 m³. The list shows the difference of 14 m³ and asks: “Which measurement is the quantity in the invoice based on?” Whether the difference is an error, a part measured later or an item from a variation, the checker clarifies with the contractor.

The entry in the monthly report to the client can then be drawn from the approved figures (see Preparing the monthly client report).

Checking and payment deadlines, in general terms

Deadlines depend on the contract. As references: under the VOB/B, claims to interim payments fall due within 21 days of receipt of the statement (section 16(1) no. 3). The claim to final payment falls due promptly after checking and determination, at the latest within 30 days of receipt of the final invoice, or within 60 days at most where that is objectively justified and expressly agreed (section 16(3) no. 1). If objections to the verifiability of the final invoice are not raised with reasons by the end of that period, the client can no longer rely on the invoice not being verifiable.

For the construction contract under the BGB the following applies to the final invoice: the remuneration is to be paid when the work has been accepted (or acceptance is not required) and the contractor has issued a verifiable final invoice. The invoice is verifiable if it contains a clear statement of the work carried out and is comprehensible to the client. It is deemed verifiable if the client raises no reasoned objections within 30 days of receipt (section 650g(4) BGB).

Which deadline starts when in your case, and what it triggers, your legal adviser clarifies from the contract. An AI can read the date of receipt from an email. The deadline calendar, however, belongs in your fixed system, and a person keeps it up to date.

What this can bring in time

As the author’s working assumption, not measured, about 45 minutes per invoice are assumed in client-side project management and about 2 hours in site supervision. The AI takes over only part of this: the comparison, finding the source references and preparing the queries. For project management I assume 20 to 35 per cent less time, for site supervision 16 to 28 per cent. Both ranges are assumptions without measurement and without a source. Arithmetically that gives 9 to 16 minutes per invoice in project management and 19 to 34 minutes in site supervision.

todaywith AI preparation

• Check, project managementAssumption, 20 % less

  today 45 min
  with AI preparation 36 min

• Check, site supervisionAssumption, 16 % less

  today 120 min
  with AI preparation 101 min

Source: The author’s working assumption, not measured

Text version of the graphic

• Check, project management: today 45 min, with AI preparation 36 min (Assumption, 20 % less)
• Check, site supervision: today 120 min, with AI preparation 101 min (Assumption, 16 % less)
• Source: The author’s working assumption, not measured

The graphic shows the lower end of the ranges, so 36 and 101 minutes. The professional determination, the queries to the contractor and the approval have not become shorter in it. Whether the assumptions fit your case only shows in your own invoices, which you time with a stopwatch before and after.

The process at a glance

The second graphic sums up who works in which step. The AI only prepares the deviation list. A fixed program does the recalculation, and everything else stays with the checker: reading the findings in the original, querying the contractor and recommending the payment.

1. Gather documents Invoice, BoQ, measurement, variations, payment status
2. Deviation list The AI matches items and enters source references AI prepares
3. Recalculate A fixed program calculates, the language model does not
4. Compare the findings The checker reads every source reference in the original
5. Query and approval The checker queries the contractor and decides on payment

Text version of the graphic

• 1. Gather documents: Invoice, BoQ, measurement, variations, payment status
• 2. Deviation list: The AI matches items and enters source references (the AI prepares)
• 3. Recalculate: A fixed program calculates, the language model does not
• 4. Compare the findings: The checker reads every source reference in the original
• 5. Query and approval: The checker queries the contractor and decides on payment

What the preparation does not replace

The deviation list does not value any work and does not determine an amount payable. It does not read drawings, and it does not measure quantities on site. It is neither legal advice nor an expert opinion. The check note, the payment recommendation and the approval stay with the person who signs for them.

Invoices contain prices and details about the parties involved. They are processed only on a platform that can be operated in line with the GDPR, not in a consumer chat service. Whether a data processing agreement is needed is for your data protection officer to clarify.

What you can do now

1. For the next five interim payment applications, measure separately how long comparing, recalculating and querying take.
2. Decide which documents belong with every invoice, and keep invoice, measurement, bill of quantities and payment status in one place.
3. Build a spreadsheet with open formulas for the five checks above and test it on an old, closed invoice.
4. Enter the checking and payment deadlines from your contracts in a deadline calendar and have your legal adviser confirm them.