Carbon accounting in Excel vs software: when spreadsheets stop working
Excel is fine for a first inventory but strains under multiple sites, verification and CBAM data. What the Commission's guidance says about spreadsheets, common errors, minimum rules and how to plan a move to software.
Carbon accounting in Excel works for a first inventory at a single site with few emission sources and nobody verifying it. It stops working when several sites and departments feed the numbers, when emission factors change from year to year, when an EU buyer asks for CBAM data per product, and when a verifier asks where a figure came from. The problem is not that a spreadsheet cannot calculate. The problem is that it does not, by itself, keep the trail of the data, who changed what, and which factor was used.
This is not an anti-Excel article. Most companies start carbon accounting in a spreadsheet, and that is a reasonable place to start. Below we look at what the European Commission's CBAM calculation guidance (Guidance No. 3, 14 August 2026) says about spreadsheets, where Excel holds up, where it breaks, and how to plan a move. We also cover product-level CBAM data, which is where the jump is hardest. We write from the perspective of Turkish producers supplying EU buyers, but the logic applies to any non-EU installation.
When is Excel good enough?
Not every company needs software. If most of the following describe you, staying in Excel is a sensible decision:
- One site, one legal entity,
- A small number of emission sources (a few fuels, electricity, company vehicles),
- One person collects the data and does the calculation,
- The report is for internal use, with no independent verification,
- No EU buyer has asked for CBAM data, or your goods are outside CBAM.
Once those conditions change, it is time to review the method rather than extend the spreadsheet.
What does the Commission's CBAM guidance say about spreadsheets?
The Commission's guidance does not ban Excel, but it names the risk plainly. Where staff read a value, write it in a journal and then transfer it by hand into a spreadsheet that is not well protected against unwanted editing, the guidance sees significant risks in the data flow that call for specific control procedures. As a better data source it points to systems that deliver values automatically to a database, without danger of manipulation. Its examples of risk also include copy-and-paste errors from a paper production journal into a spreadsheet, and data on a computer that is freely accessible to all staff.
The same guidance expects a control system alongside the monitoring plan. A company relying on spreadsheets should think through how it will meet each point:
| What the guidance expects | What that means in Excel |
|---|---|
| Risk assessment of the data flow, from primary data to final data | Every link between files and every manual transfer is a risk point to write down. |
| Quality assurance of IT systems | You design the formula testing and sheet protection yourself. |
| Segregation of duties and the "four-eyes" principle | Preparer and reviewer must differ, and you keep the review record by hand. |
| Internal review and validation of data | Completeness and consistency checks are extra formulas you must build. |
| Management of document versions | This relies on naming discipline; the "final_v3_really.xlsx" trap starts here. |
| Records kept at least six years after the reporting period | Formulas and linked files must still open and make sense six years on. |
The guidance adds that the better the control system, the less effort the verifier needs. So these points are not only about compliance; they also shape the time and cost of verification. For where verification fits in the process, see how to prepare a CBAM report.
Where does carbon accounting in Excel usually break?
Spreadsheet errors are not specific to carbon. Ray Panko's review of field audits reports that audits using better methods found errors in at least 86% of the spreadsheets examined. A 2009 study by Powell, Baker and Lawson found errors in 0.9% to 1.8% of formula cells across 50 operational spreadsheets. The rates depend on method and definition, but the shared finding is that errors in large spreadsheets are to be expected, not an exception. In carbon accounting, they typically look like this:
| Failure point | What happens | Result |
|---|---|---|
| Mixed units | Natural gas entered in m³ one month and kWh the next; kg and tonnes confused. | Results off by a large factor, and easy to miss in the total. |
| Stale emission factor | Last year's sheet is copied and the factor is not updated. | Year-on-year comparison breaks down. |
| Unsourced factor | A cell says 2.02, with no source or year. | You cannot justify it to a verifier. |
| Broken formula range | A new row is added outside the total's range. | A source silently drops out of the calculation. |
| File sprawl | Energy, logistics and procurement each work in their own copy. | Nobody is sure which file is current. |
| Key-person dependency | The person who built the workbook leaves. | The logic has to be reverse-engineered. |
Why do corporate inventories and CBAM strain the same spreadsheet?
The real jump comes when you move from a corporate footprint to per-product numbers. Scope 1, 2 and 3 and ISO 14064-1 inventories are company-wide and annual. CBAM works by installation, production process and good. You have to attribute emissions to processes, add the embedded emissions of purchased precursors, divide by production, and tie each good to its CN code. With a multi-step precursor chain, or heat shared between processes, the number of links between sheets grows quickly.
Keying the same fuel and electricity data into two separate files is a risk of its own: when two reports show different figures for the same site, you will have to explain why. Try laying out the steps in our steel embedded emissions guide in a workbook and you will see the structure repeat for every product.
Base years and factor updates: the hidden workload
The GHG Protocol Corporate Standard ties transparency to a clear audit trail and asks companies to set a policy for when the base year is recalculated. Structural changes such as buying or selling a site, improvements in method or data accuracy, and the discovery of a significant error can all trigger a recalculation. In Excel, that means reopening past workbooks one by one. The same applies when you change a factor source (DEFRA to a national dataset, say) or a global warming potential set (IPCC AR5 to AR6): earlier years still need to stay comparable.
If you stay in Excel: the minimum rules
- Separate inputs, factors and calculations. Three sheets, with no typed numbers on the calculation sheet.
- Add a source column to every row. Invoice number, meter record, document path.
- Keep factors in one place. Value, unit, source, year and access date.
- Restrict units with data validation. Use drop-down lists, not free text.
- Lock calculation sheets. Give edit rights to one person.
- Apply the four-eyes principle. Someone other than the preparer reviews, and the review is recorded.
- Freeze the file at period close. Archive it read-only; make corrections in a new version with the reason noted.
- Add consistency checks. Monthly against annual totals, deviation from last year, meter against invoice.
Signs it is time to move to software
- An EU buyer has asked for embedded emissions per product, or soon will.
- You have more than two sites, or several departments entering data.
- Your inventory will go through independent verification.
- Rebuilding the workbook takes weeks every year.
- Only one person understands the spreadsheet.
- Last year's figure appears with three different values in three files.
| Criterion | Excel | Carbon accounting software |
|---|---|---|
| Upfront cost | Low | Licence and setup needed |
| Flexibility | High, you can build anything | Method is ready-made; limits depend on the product |
| Emission factors | Found and updated by hand | Selected from a library, source recorded |
| Access rights | By file | By role and department |
| Multiple sites | Merging files | Tracked in one structure |
| Link to CBAM | A separate model to build | Varies by product; ask before you buy |
Software is not a cure on its own: a wrong meter reading gives a wrong result in any system. When you evaluate a tool, enter one of your own invoices during the demo and trace how the result is built.
How to plan the move from Excel to software
- Take stock. Which files exist, who fills them in, and where does the data come from?
- Map the data flow. Write down every step from invoice to result. This is also the basis of a CBAM monitoring plan.
- Clean up your factors. Replace unsourced values with ones from a reliable source.
- Assign roles. Who enters, who reviews, who approves?
- Run one period in parallel. Calculate the same year both ways and explain the differences. If a difference reveals an error, consider the base year.
- Update your documents. The data flow has changed, so revise the monitoring plan and procedures, and tell your verifier in advance.
How Carbonet approaches this
Carbonet is a corporate carbon footprint and CBAM software developed by LNA Soft in Izmir, Turkey. You can choose IPCC AR5 or AR6 and DEFRA, EPA or TÜİK (Turkish Statistical Institute) factor sources, and the source and factor version behind each figure stay on record. Each department enters and sees only its own data, and all sites are tracked on one screen. The fuel, electricity and process data you enter for your ISO 14064 GHG inventory flows into the CBAM embedded emissions calculation, so you do not enter it twice.
Bring your current workbook and we will look at it together: request a demo, or write to info@carbonet.com.tr or WhatsApp +90 533 368 05 99.
Frequently asked questions
Can you do carbon accounting in Excel?
Yes. A single-site inventory with few sources and internal use can be prepared in Excel. Once source records, factor management, access control and a verification trail matter, spreadsheet discipline may no longer be enough.
Can CBAM data be prepared in Excel?
The Commission's guidance does not prohibit spreadsheets. It does say that manual transfers and poorly protected spreadsheets create significant data-flow risks that need specific control procedures. If you use Excel, those controls should be written down and be able to be shown to your verifier.
How long must CBAM records be kept?
According to the Commission's calculation guidance of 14 August 2026, monitoring records relevant to embedded emissions and the supporting documentation must be kept for at least six years after the reporting period. The calculation should remain traceable throughout that time.
When should a company move to software?
Consider it when an EU buyer asks for per-product data, when several sites or departments enter data, when the inventory will be independently verified, or when only one person understands the workbook. Company size alone is not the deciding factor.
What happens to past data held in Excel?
The soundest approach is to calculate one reporting period both ways and explain the differences. If a difference reveals an error, check your base year policy to see whether a recalculation is needed. Keep the old workbooks as records.