MITECO emission factors in 2026: which version to use and how to apply them

Spain's Ministry for the Ecological Transition, MITECO, publishes its emission factors in early May each year, and the rule for using them is simple: apply the factors for the year you are calculating, and only if those have not been published yet may you use the latest available year. The version released in May 2026 is the one that carries the factors for 2025, the financial year most companies are closing now. The official organisational carbon footprint calculator, version 17 of May 2026, covers the factor series from 2007 to 2025.

It sounds obvious, and it is the single most repeated mistake: calculating a 2025 footprint with last year's factor document because that is the file sitting in the shared folder.

What MITECO publishes and what each document is for

The Spanish carbon footprint, offsetting and absorption projects registry maintains a set of documents worth telling apart:

• Emission factors. The annual document with values by source and by year. This is the one you cite in your calculation memo.
• Official calculators. Spreadsheets for organisations, municipalities and farms, plus the reduction calculator and the absorption projects calculator. The organisational calculators cover scopes 1 and 2 only.
• Instructions for each calculator. A living document, with version number and date, explaining which factors it incorporates and what has changed.
• Support document for registration. Sets out the requirements for the seal and the accepted calculation rules.
• Questions and answers. Resolves the real edge cases, and is where the answers people hunt for in forums actually live.

Before you start calculating, note the version and date of every document you use in your calculation memo. It is the first thing an assurance provider asks for and the last thing that tends to be written down.

The electricity factor: what has to be right

There is no room for interpretation here. The registry establishes that indirect emissions from electricity consumption must be calculated in every case using the electricity mix factors the registry itself provides, which are in turn the ones published by the CNMC, Spain's markets and competition authority.

Step by step:

1. Identify your electricity retailer at each supply point. It is on the invoice, not in a contract signed five years ago.
2. Look that retailer up in the registry's list. If it appears, use its specific factor, which reflects that retailer's mix and its guarantees of origin.
3. If your retailer is not on the list, or you do not know it, use the generic "Otras" factor. Do not invent an intermediate value or apply the national mix on your own initiative.
4. If you switched retailer mid-year, apply each factor to the kilowatt hours actually bought from that retailer, and document the split.

That distinction between the retailer's factor and the general mix is what makes two companies with identical consumption report very different emissions. How guarantees of origin work behind that factor is explained in the glossary entry on guarantees of origin.

Fuels, refrigerants and vehicles

The three other blocks that generate the most questions:

The critical point on refrigerants is where the data comes from: the annual recharge appears on no energy invoice, it is in the maintenance report. If your contractor does not provide it broken down by equipment and by gas, ask in writing before year end.

Five common mistakes and how to avoid them

1. Mixing years. Calculating 2025 with the previous year's factor document because "it barely changes". If you do it because the new one is not out, say so and apply the latest-available-year rule explicitly.
2. Using DEFRA factors without justification. For electricity consumed in Spain it does not apply: the registry requires its own mix factors. For categories MITECO does not cover, another source may be reasonable, but you have to state which one, from which year, and why.
3. Double counting guarantees of origin. Applying the reduced factor of a retailer with guarantees and then also deducting the renewable energy contracted. It counts once.
4. Using the national mix when your retailer is on the list. It overstates emissions and it is incorrect under the registry's own criteria.
5. Leaving no trace of the version. The memo says "MITECO factors" with no version and no date. With that, an assurance provider cannot reproduce the calculation, and reproducing it is precisely the job.

How to document the choice for assurance and for the registry

A one-page table answers most of a verifier's questions. For each emission category, write down:

• The source of the factor, with the full document name.
• The version and date of that document, as printed on its cover.
• The year the factor corresponds to.
• The value and unit applied.
• The justification, where the factor is not the default one: retailer not listed, category not covered, change of supplier mid-year.

Keep that table next to the calculation file, not in an email. The registration process and the seals are covered in the guide to the MITECO registry and the Calculo, Reduzco and Compenso seals, and the failures that cause most rejections are in the article on the five most common mistakes when certifying your carbon footprint with MITECO.

How this connects to Royal Decree 214/2025

Royal Decree 214/2025 requires companies in scope to calculate their scope 1 and 2 carbon footprint, with scope 3 voluntary, and to have a reduction plan with a five-year horizon and quantified targets. It applies to companies with more than 250 employees that are public-interest entities, or that exceed, over two consecutive financial years, €20 million in assets or €40 million in turnover.

Two points that often get confused:

• Under MITECO's clarifying note of December 2025, the footprint and the reduction plan must be published within six months of the financial year end, and the calculation may cover any twelve consecutive months.
• Registration in the MITECO registry remains voluntary for private companies. Only state public sector entities are required to register. Calculating and publishing is mandatory for those in scope; registering is not.

The full scope of that obligation is set out in the article on carbon footprint registry obligations under Royal Decree 214/2025, and the split between scopes in the explanation of the differences between scope 1, 2 and 3 emissions.

Checklist before you close the calculation

Run through these seven points before signing off the number. Each one maps to a failure that shows up repeatedly in reviews:

1. The version of the factor document you used is written down, with its date, and matches the year you are calculating.
2. Every electricity supply point has its retailer identified from the period's invoice, not from an old list.
3. Retailers absent from the registry's list have been treated with the generic factor, and it is justified in writing.
4. Fuel consumption is recorded in litres or kilograms with documentary support, not converted from amounts using an invented average price.
5. The year's refrigerant recharges are captured per unit of equipment and per gas, backed by the maintenance report.
6. Vehicles are classified from their technical data sheet, not from whichever category seems most reasonable.
7. There is no figure in the spreadsheet that cannot be traced to a source document.

If any of those seven fails, the number may still be roughly right, but it will not be defensible. The full calculation method, from boundary to report, is in the guide to what a carbon footprint is and how to calculate it.

Frequently asked questions

Which factor version do I use to calculate 2025?

The one published in 2026, which carries the series up to year 2025. The general rule is to use the factors of the year you are calculating and, if they are not yet published, those of the latest available year.

When does MITECO publish each year's factors?

In early May. If you close your footprint before that, apply the latest-available-year rule and write it down.

Can I use the national mix factor instead of my retailer's?

Not if your retailer appears in the registry's list. In that case its specific factor applies. If it does not appear, the generic "Otras" factor is used.

Do the MITECO calculators cover scope 3?

The organisational carbon footprint calculators cover scopes 1 and 2 only. Scope 3 is calculated separately.

Do I have to register if Royal Decree 214/2025 applies to me?

No. Registration remains voluntary for private companies. What is mandatory is calculating scopes 1 and 2, having the reduction plan, and publishing on time.

Can I change factor source between years?

You can, but it has to be explained, and you should consider whether the base year needs restating so the series stays comparable. A silent change is a guaranteed finding.

Applying the right factor is easy when the system knows each supply point's retailer and the current factor version. Our carbon footprint solution maintains that mapping and records which factor was applied to each data point, and why.