The verdict in three sentences
A general contractor with EUR 40 million in revenue managing 120 subcontractors in Excel spends 3 to 5 days a month building progress billing and risks costly errors on retention, direct payment and social security compliance certificates. Construction ERPs (Onaya, Batappli, Sage) handle client billing well, but detailed subcontractor management often remains a blind spot. A custom module at EUR 30,000 to 80,000 excluding VAT, connected to your ERP, secures compliance and cuts closing time by 60 to 70%.
The risks of running subcontracting in Excel
In a city like Toulouse, office, housing and aerospace projects generate sites worth EUR 2 to 15 million where the general contractor coordinates 15 to 40 trade packages. Every month, billing must be consolidated, price indexation applied, retention withheld and legal documents checked. The rules below are French; most European markets have close equivalents.
| Obligation or task | 2026 rule (France) | Risk if mishandled |
|---|---|---|
| Retention | 5% maximum (law of 16 July 1971), released within 1 year or replaced by bank guarantee | Dispute, late interest |
| Direct payment of subcontractor | 1975 law, public contracts above EUR 600 incl. VAT | Double payment or client blocking |
| URSSAF compliance certificate | Check every 6 months from EUR 5,000 contract value | Joint financial liability of the main contractor |
| VAT reverse charge | Construction subcontracting invoices without VAT | Tax reassessment |
| BT01 price indexation | Monthly INSEE index, contractual formula | Margin loss of 1 to 3% on long projects |
| Payment terms | 60 days from invoice or 45 days end of month | Penalties, EUR 40 fixed fee per invoice |
Construction ERP or custom module: the 2026 comparison
| Criterion | Onaya | Batappli | Sage construction | Custom module |
|---|---|---|---|---|
| Target | SMEs and mid-caps | Small firms and SMEs | SMEs and mid-caps | Mid-caps with own processes |
| Annual cost (25 users) | EUR 15,000 to 30,000 | EUR 5,000 to 12,000 | EUR 12,000 to 25,000 | EUR 4,000 to 9,000 maintenance |
| Client progress billing | Yes | Yes | Yes | Read from the ERP |
| Subcontractor billing consolidated by package | Partial | Basic | Partial | Yes, by site and package |
| Automatic compliance and registry checks | Option or partner | No | Option | Yes, via certificate API |
| Direct payment and payment delegation | Partial | No | Partial | Yes, workflow with project owner |
| Automatic BT01 indexation | Yes | Partial | Yes | Yes, contractual formulas per contract |
| Subcontractor portal (billing upload, documents) | Limited | No | Limited | Yes |
Costs are 2026 orders of magnitude; ERP licences depend on users and modules enabled.
Custom module budget
| Tier | Scope | Timeline |
|---|---|---|
| EUR 30,000 | Subcontractor billing, retention, reverse charge, accounting export | 10 to 12 weeks |
| EUR 50,000 | + automated compliance checks, BT01 indexation, payment term alerts | 14 to 18 weeks |
| EUR 80,000 | + subcontractor portal, direct payment with project owners, margin dashboard per site | 20 to 26 weeks |
| Maintenance | Hosting in France, regulatory updates | EUR 350 to 750 per month |
| ERP connector | Link with Onaya, Sage or Batappli | EUR 4,000 to 10,000 |
Mini case study
Thomas, finance and administration director of a Toulouse general contractor (EUR 40 million revenue, 120 active subcontractors), has 2 accountants spend 4 days every month on progress billing, 768 hours a year. At a loaded cost of EUR 45 per hour, that is EUR 34,560. A BT01 indexation error on a EUR 6 million project cost him 1.5% of margin, EUR 90,000. He chooses the EUR 50,000 tier plus a EUR 6,000 connector and EUR 500 monthly maintenance. With 65% of time saved (EUR 22,460 a year) and a single indexation error avoided, the EUR 62,000 first-year investment is covered in under 12 months.
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FAQ
How much does subcontractor progress billing software cost?
EUR 30,000 to 80,000 for a custom module depending on scope, plus EUR 350 to 750 per month of maintenance. A full construction ERP costs EUR 5,000 to 30,000 a year in licences.
Do we need to replace our construction ERP?
No. The module connects to Onaya, Sage or Batappli to pull contracts, packages and entries. You keep your ERP for client billing and accounting.
How are compliance checks automated?
The module queries a certificate collection platform and blocks payment if the compliance certificate is older than 6 months. This protects the main contractor from joint liability from EUR 5,000 of contract value.
Is BT01 indexation calculated automatically?
Yes: the INSEE index is fetched monthly and applied according to each contract's formula. On an 18-month project, the avoided gap often equals 1 to 3% of the contract value.
How long until go-live?
From 10 to 26 weeks depending on the tier, with a pilot on 2 or 3 sites before rolling out to all 120 subcontractors.
Let's scope your project. Tell us your ERP, number of sites and subcontractors: we will price the scope, indicative budget and rollout timeline. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
