- 1The V9 method, Base Empreinte and basic tools are free, but account for only about 20% of the work.
- 2For an SME with 50 to 250 employees, an in-house assessment represents €30,000 to €48,000 in fully loaded person-days.
- 3With Diag Décarbon'Action, the consultancy costs €6,000 excluding VAT in out-of-pocket costs, less than an in-house assessment for most SMEs.
- 4An in-house approach is justified in 2 cases: a mature CSR team of at least 2 FTEs, including one trained by ABC, or a micro-business with fewer than 10 employees taking an educational approach.
- How much does doing your own Bilan Carbone® really cost?
Technically feasible, rarely economical.
- 30 to 80 person-days internally for a first assessment, equivalent to €15,000 - €48,000 excl. VAT depending on size.
- Compare this with €10,000 - €30,000 excl. VAT for a consultancy service or €6,000 excl. VAT with Diag Décarbon'Action.
- 2 cases where an internal assessment makes sense: a mature CSR team or a very small business using it for learning.
1Why an in-house assessment looks free
3 building blocks of the Bilan Carbone® method are accessible free of charge. The method itself, in its V9 version in force since 1 January 2025 and managed by the Association pour la transition Bas Carbone (ABC), is documented in freely accessible materials, including the application manual: any company can download and follow it.
Emission factors, which convert consumption (kWh of electricity, km travelled, kg of steel purchased) into tonnes of CO2 equivalent (tCO2e), can be consulted free of charge on ADEME's Base Empreinte, without a licence or subscription.
ADEME tools (simplified assessments for small organisations, sector calculators and data collection spreadsheets) can be downloaded free of charge, and Bilan Carbone® spreadsheets are supplied at no additional cost to entities training in the method through ABC.
It is easy to conclude that the assessment is free. But the method, factors and tools account for only about 20% of an assessment's value; the rest comes from the time spent and the team's expertise.
2The real cost: 30 to 80 internal person-days
Here are the orders of magnitude we observe on the French market, based on assessments that in-house teams end up asking us to review or audit.
For a company with 10 to 50 employees, allow 30 to 50 person-days for a first documented scope 1, 2 and 3 assessment: initial training (3 to 5 days), mapping flows (5 to 10 days), data collection (15 to 25 days), modelling and presentation (7 to 10 days). Converted into the full loaded cost (around €500 per day for a junior CSR manager, including employer contributions), this represents an equivalent budget of €15,000 to €25,000, excluding time taken from other departments.
With 50 to 250 employees, allow 50 to 80 person-days. Scope 3 becomes more complex (more suppliers and more material categories), collection across departments takes longer and the analysis requires more cross-checking. At €600 per day (an experienced CSR manager), this represents an equivalent budget of €30,000 to €48,000.
In a mid-cap with 250 to 1,000 employees, the figure rarely falls below 150 person-days spread across several contributors. At this size, the assessment becomes a team project involving CSR, purchasing, logistics, finance and IT. The equivalent budget often exceeds €80,000, and the question is then less about choosing an in-house approach than about making the process systematic.
For comparison: a standard consultancy service for an SME costs between €10,000 and €30,000 excluding VAT, depending on complexity (price ranges by size in detail), and falls to €6,000 excluding VAT in out-of-pocket costs with Diag Décarbon'Action for eligible entities.
33 blind spots of an in-house assessment
Beyond the cost in person-days, three areas quietly affect the quality of an assessment carried out without external help.
The method changes faster than CSR teams. Bilan Carbone® V9 has applied since 1 January 2025, following a trial phase launched in July 2024; the ESRS, including E1 for climate, adopted in 2023, were simplified after the Omnibus Directive, with a revised version adopted by the Commission in 2026; Base Empreinte is updated 2 times a year and the GHG Protocol publishes regular revisions. A generalist CSR team can easily miss one of these developments, and an assessment based on an outdated version of the method or factors is rejected as soon as it goes before a statutory auditor or a demanding client.
Scope 3 requires prioritisation expertise. The 15 scope 3 categories do not carry the same weight in every activity. Treating everything in detail costs too much; approximating everything produces an unusable assessment. The real skill is knowing which categories are material (to be handled using physical data), which can use monetary ratios, and which can be excluded with justification. This prioritisation is not in the manual: it is acquired over 20 to 30 real assessments.
Interpretation and the action plan. A useful assessment does not stop at a figure: it leads to a trajectory, priorities and trade-offs. Yet a team that has just spent 60 days collecting data often lacks the energy and perspective for this work, which determines whether the assessment will help guide decisions.
4The 2 cases where an in-house assessment makes sense
Case 1 - A mature CSR team with at least 2 FTEs, including one trained by ABC. In a large company or mid-cap that has already produced 2 or 3 assessments, the logic reverses: the team knows the method, the data are already mapped and the tools are deployed. Outsourcing costs more than it delivers, and an annual in-house assessment becomes the right frequency, with occasional consultancy input on technical issues (method overhaul, third-party verification, external audit). To develop this capability, see the Bilan Carbone® training offered with IFC.D, including levels and prerequisites.
Case 2 - A micro-business with fewer than 10 employees taking a voluntary educational approach. When the main aim is internal awareness, discovering the subject and an initial indicative diagnosis, a simplified assessment using ADEME spreadsheets over 3 to 5 person-days is enough. It remains approximate, but starts an internal discussion, which is the main aim at this size.
Outside these two cases, a 100% in-house assessment produces knowledge (good) and data that are rarely usable externally (less good). Last year, we audited the scope 1+2+3 assessment of a mid-cap with 400 employees that had produced it entirely in-house over 9 months. The method was impeccable and data collection very clean. The problem lay elsewhere: scope 3 category 1 (purchases) had been handled exclusively using INSEE monetary ratios across 18 purchasing families. As a result, 78% of emissions were concentrated in a category that could not be managed. Remodelling with physical data for the 6 material families took 11 consultancy days (€7,500 excluding VAT), and revealed 3 tangible decarbonisation levers invisible in the first assessment. The in-house approach was sound; it lacked an outside perspective accustomed to spotting these categories.
5External service versus in-house assessment: 2026 cost comparison
For an SME with 50 to 250 employees in 2026, the 3 options compare as follows. A 100% in-house assessment represents an equivalent budget of €30,000 to €48,000, takes 9 to 12 months, has moderate external credibility (unless reviewed by a third-party consultancy at the end) and offers no structured action plan. A standard consultancy service costs €10,000 to €30,000 excluding VAT in invoiced fees, takes 4 to 6 months and offers strong credibility and an included action plan. Diag Décarbon'Action costs €6,000 excluding VAT in out-of-pocket costs (€4,000 funded by Bpifrance and ADEME), takes a maximum of 10 months, and offers the same credibility and an included action plan.
On paper, the in-house option costs nothing. Converted into the budget it consumes, it is nevertheless the most expensive option for most SMEs, unless the team already has the maturity described above.
6How Diag changed the decision
Diag Décarbon'Action, a Bpifrance/ADEME scheme launched in 2021, open to SMEs with <500 employees, including micro-businesses, and at least 1 year in business, has structurally shifted the decision point. With out-of-pocket costs of around €6,000 excluding VAT for a full assessment delivered by an ABC-certified consultancy, the external service becomes cheaper than the equivalent internal budget for almost all eligible SME profiles. For this segment, the economic argument for a "free in-house assessment" no longer holds.
The choice remains valid for ineligible entities (too young, more than 500 employees, previous beneficiaries) and those with the in-house maturity described above. For the others, the remaining decisions concern assessment frequency (every year or every 4 years) and its coverage (with or without scope 3).
7Before starting an in-house assessment
For a standard SME, an in-house assessment costs €0 on paper, but an equivalent budget of €30,000 to €48,000 once the 30 to 80 fully loaded person-days are counted (collection, modelling, presentation). With Diag Décarbon'Action, the same deliverable, produced by an ABC-certified consultancy, costs around €6,000 excluding VAT, removing most of the economic attraction of an in-house assessment for eligible SMEs. An in-house assessment remains meaningful in 2 specific cases: a mature CSR team with someone trained by ABC (at least 2 dedicated FTEs), or a micro-business with fewer than 10 employees taking an educational approach.
Before setting up an in-house assessment team, first check your Diag eligibility, then compare the 2 full costs over 12 months: the calculation is often enough to decide.
