Progress invoices with Claude: check cumulative amounts and the difference
Architect progress invoice: bill a difference, not a cumulative total, with mandatory mentions and progress-calculation methods.
By Educasium
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An architect is following a renovation site where the contract calls for progress-based invoicing, approved at a monthly site meeting. After the third progress invoice, the client is surprised: the total of the invoices issued already exceeds, in their view, the actual progress of the site. Reviewing the file, the architect discovers that the latest invoice was calculated on the month's progress alone, without deducting what had already been billed in previous months — a plain duplication, invisible until someone reconstructs the cumulative total from the start.
A progress invoice does not bill the month's progress: it bills the difference between the cumulative progress recognized to date and what has already been billed before. This distinction, simple as it looks, is the most frequent source of error in tracking the finances of a commission billed by phase or by progress — and an error repeated across several successive invoices can end up billing a total higher than the contract value, long before the final invoice that should close the commission.
This article details what sets a progress invoice apart from a simple progress record, the mandatory mentions it must carry, the different methods for calculating its amount depending on the fee method chosen, and a method for building it without creating a duplication.
Summary
- A progress invoice bills a difference, not a full cumulative total
- Mandatory mentions do not change from one invoice to the next
- Choosing the right progress-calculation method
- Building a progress invoice step by step
- When a progress invoice is not enough
- What we observe among independent architects
- Training to make invoicing more reliable
- Frequently asked questions
A progress invoice bills a difference, not a full cumulative total
A progress invoice records a payment right corresponding to the commission's progress since the last invoice — never since the start of the contract. Confusing the cumulative value recognized to date with the amount of the new progress invoice alone amounts to re-billing a part of the commission already settled by an earlier invoice.
What sets cumulative recognized value apart from previously billed value
A progress invoice's amount is always obtained by subtraction: cumulative value recognized at the chosen date, minus the total already billed on earlier progress invoices and the deposit. Fictional example excluding tax: a €10,000 contract reaches approved progress of 60%, or a cumulative recognized value of €6,000. Earlier invoices — deposit and previous progress invoices combined — already total €4,000. The new progress invoice to issue is therefore €2,000 excluding tax, never €6,000, which would wrongly repeat an amount already billed.
Why confusing received payments with billed amounts creates a duplication
A progress invoice remains due, and therefore still counts toward the total already billed, even if the client has not yet paid earlier invoices: tracking unpaid amounts is a separate matter, to be handled on its own, never by recalculating the billed cumulative total from receipts actually received. Treating an unpaid earlier invoice as if it had never been issued would lead to billing it a second time in the next progress invoice — a duplication the client, by reconciling the documents themselves, always ends up spotting.
Mandatory mentions do not change from one invoice to the next
A progress invoice carries the same mandatory mentions as a deposit invoice or a final invoice: it is not a lightweight document simply because it sits in the middle of an invoicing sequence.
Identity, VAT and numbering
Article L441-9 of the French Commercial Code requires the full identity of the parties, the issue date, a precise description of the invoiced service and its price excluding tax; for an architect, this is supplemented by the registration number with the Ordre and the reference of the ten-year insurance required under Article L241-1 of the French Insurance Code. A VAT-liable architect applies 20% VAT on the tax-excluded amount, under Article 278 of the French General Tax Code; an architect under the VAT exemption scheme instead carries the mention "TVA non applicable, article 293 B du CGI". Numbering must stay continuous with the deposit invoice and earlier progress invoices for the same commission, never restarting a separate sequence for "progress invoices."
Linking each progress invoice to the contract and to earlier invoices
A progress invoice must carry the contract reference, but also that of the deposit invoice and the last progress invoice issued, so the whole invoicing chain stays checkable from one document to the next. Without this explicit link, reconstructing the exact cumulative amount billed on a long commission — often spread across several months, with monthly progress invoices — becomes a manual reconstruction exercise, prone to error.
Choosing the right progress-calculation method
The project-management contract determines the progress-calculation method, and that method is never chosen after the fact, at the moment the invoice is issued.
| Calculation method | Basis used | When to use it | Frequent pitfall |
|---|---|---|---|
| Breakdown by phase | Fixed percentage assigned to each phase (ESQ, APS, PRO…) contractually | Commission split into standardized phases with a weighting set in the contract | Billing a phase that has started as if it were fully complete |
| Observed physical progress | Actual site progress percentage, approved at a meeting | Commission with site supervision and regular progress checks | Using a percentage estimated verbally without written approval |
| Time spent (time and materials) | Hours or days actually worked, at the contractual rate | Time-and-materials commission, with no overall lump sum defined | Billing estimated time instead of actually logged time |
| Calendar milestones | Fixed dates set out in the contract, independent of actual progress | Contract with calendar milestones rather than progress-based billing | Billing a calendar milestone when the contract actually called for progress-based billing |
Building a progress invoice step by step
Building a reliable progress invoice follows a precise order, which prevents discovering after issue that an amount did not match the actual cumulative value.
Step 1: Gather the contract and every invoice already issued. The deposit and all earlier progress invoices must be collected, not just the last one: the cumulative total is reconstructed over the whole commission, never from the previous invoice alone.
Step 2: Determine the cumulative value recognized at the chosen date under the contractual method. The percentage or time spent needs a verifiable source — approval at a site meeting, a logged timesheet, a signed schedule — never an unsupported estimate.
Step 3: Subtract the total already billed from the recognized cumulative value. The progress invoice's amount is that difference, excluding tax and then including tax once the applicable VAT rate is applied.
Step 4: Check for credit notes or corrections before the final calculation. A credit note issued on an earlier invoice must be folded into the total already billed before calculating the new difference, or the cumulative total is distorted.
Step 5: Number, reference and issue the invoice. The contract reference, the deposit invoice reference and the previous progress invoice reference must appear on the document, so the invoicing chain stays traceable through to the final invoice.
When a progress invoice is not enough
A correctly calculated progress invoice does not resolve every situation that can arise during a commission.
An amendment still under negotiation, not yet formally accepted by the client, must never be folded into a progress invoice's cumulative total before its written acceptance: pre-billing an amount tied to an unconfirmed change creates a risk of immediate dispute. A disagreement between the architect and the client over the actual site progress percentage is not resolved by issuing the invoice either: it calls for a prior clarification, possibly a new joint site meeting, before any further invoice is issued. A negative calculation result — a recognized cumulative value lower than the total already billed — almost always signals earlier overbilling or a downward revision of progress, a situation that should be analyzed with an accounting professional before any invoice is issued or corrected. A draft invoice prepared with AI assistance remains, in every case, a draft document: it must be reviewed and approved before issue.
What we observe among independent architects
In our exchanges with independent architects about invoicing during a commission, the sticking point is almost never the calculation logic itself: an architect knows a progress invoice bills a difference. What costs time is manually reconstructing the cumulative total on long commissions — retrieving every earlier invoice, checking that no credit note was missed, or recalculating a progress percentage from scattered site notes. That is reconstruction work, not a lack of skill — and it is exactly the kind of task a well-built document template removes, without taking away any of the professional validation of actual progress, which remains entirely in the architect's hands.
Training to make invoicing more reliable
Setting up a progress-invoice template once and for all is not enough: it also needs to stay usable throughout an entire commission, invoice after invoice, without losing track of the cumulative total. For an architect practising as a self-employed professional (NAF code 7111Z in France), the FIFPL fund covers part of the cost of Qualiopi-certified training under 2026 criteria set at €300 per day and €900 per year, with e-learning capped at 50% of the daily rate. This funding must be arranged before training starts, not after.
Frequently asked questions
Can a progress invoice be negative?
A negative result — a recognized cumulative value lower than the total already billed — is not an invoice to issue as is: it signals an anomaly to address, most often earlier overbilling relative to actual progress, or a downward revision of progress observed since. This situation calls for reviewing the file before any decision, usually with an accounting professional's help, to determine the appropriate treatment — credit note, adjustment, or a revised schedule. Issuing a zero-value progress invoice anyway, without fixing the cause of the gap, only pushes the problem onto the final invoice, where it becomes harder to isolate among the other end-of-commission adjustments.
Should deposits be re-billed in progress invoices?
No: the deposit billed at the start of the commission is part of the total already billed, and must be deducted from the recognized cumulative value exactly like earlier progress invoices, never re-billed a second time. A progress invoice that left the deposit out of the calculation would produce an overstated amount, inconsistent with the contract total once every invoice is added up. This reconciliation must be checked on every new progress invoice, not just the first: a deposit forgotten once can stay invisible for months if no one reconstructs the full cumulative total from the start of the commission.
How do you know which progress percentage to bill?
The percentage used must always have a verifiable source, defined by the contract itself: joint approval at a site meeting, a logged timesheet for a time-and-materials commission, or a phase weighting set at signature. A percentage estimated without written approval, even in good faith, is exposed to a later dispute if the client challenges the progress used at the time of billing. Absent a recent formal approval, good practice is to request that confirmation before issuing the invoice, rather than billing on an estimate that will need justifying afterwards.
Must a progress invoice carry the same mentions as a deposit invoice?
Yes, without exception: the full identity of the parties, the Ordre registration number, the ten-year insurance reference, the applicable VAT rate and continuous numbering must appear on a progress invoice exactly as on a deposit or final invoice. Nothing about this document's intermediate nature justifies lightening the mandatory mentions required by the Commercial Code. A template that lightens these mentions for a commission's "intermediate" invoices must be corrected before any use, or it exposes the issuer to the same penalties as an incomplete deposit invoice.
What should be done if the client disputes the billed progress?
A disagreement over the progress percentage is not resolved by issuing the invoice and waiting for the client's reaction: it calls for a prior clarification, generally at a joint site meeting where progress is checked and approved by both parties. Issuing an invoice on disputed progress, without that approval step, delays resolving the disagreement rather than speeding it up, and complicates reconciling the progress invoices that follow. Documenting that meeting with a signed record, even a brief one, avoids having to reconstruct a verbal agreement from memory weeks later if the disagreement resurfaces on a later progress invoice.
A reliable progress invoice rests on three elements that do not change from one commission to the next: a calculation by difference between the recognized cumulative value and what has already been billed, never an isolated amount for the elapsed period alone, the full mandatory mentions required of any architect invoice, and an explicit link to the contract and earlier invoices. Once that foundation is in place, it is exactly what the progress-invoice generator applies automatically, difference calculation included, while leaving the architect to validate actual progress.
Earlier in the commission, our method for the deposit invoice details the first accounting document that opens the cumulative total, and later on, our final-invoice guide explains how to close the commission without re-billing what the successive progress invoices already settled.
Training 100% fundable via OPCO/FIFPL. Qualiopi-certified programme. To structure your invoicing (proposal, deposits, progress invoices, final balance) with AI as part of our AI for architectural management training, contact Educasium and specify your status (employee, self-employed, business owner) and your goal.