Until 19 October 2026 the app used the government factors for 2019 onwards, and anything older was worked out with the 2019 set. Now an entry dated 2015 uses the 2015 factors, and spend-based Scope 3 can go back to 1997.
What is covered
| Years | What the government published |
|---|---|
| 2012 to 2026 | The full set: electricity, gas and other fuels, vehicles, travel, freight, refrigerants, waste and water. |
| 2003 to 2011 | DESNZ: UK electricity, grid losses and heat and steam, with their well-to-tank lines. Defra and DECC guidelines of the time: fuels, vehicles, travel, freight and refrigerants (kg CO2 only before 2009), and from 2009 waste, water and materials. |
| 2002 | DESNZ: UK electricity and grid losses, with their well-to-tank lines. Defra's 2001 guidelines: fuels, cars, rail, flights, freight and refrigerants. |
| 1997 to 2023 | Defra's spend multipliers, kg CO2e per pound spent, by industry. |
Some lines start later even within the full sets, because DESNZ only began publishing them later: plug-in and battery electric cars from 2017, hotel stays from 2017 (every country from 2019) and flights between two airports outside the UK from 2015, for example. Each factor page shows every year DESNZ published that factor: the UK electricity page goes back to 2002 and the natural gas page to 2002, with the years before 2012 taken from the Defra guidelines. Every guideline figure is traced to the file and page or row it came from.
What the app does with older years
For 2002 to 2011, electricity and heat are calculated with DESNZ's factor for that year, and fuels, travel and the rest with the Defra guidelines in force that year (the 2001 edition for 2002 to 2004, for example), labelled as such next to every figure and in the report's method note. Where that edition has no factor, the app says so and asks you to enter the year's total directly, rather than quietly using a later year's factor. A Carbon Reduction Plan baseline before 2012 works the same way: you type in its Scope 1, 2 and 3 totals. Entries dated before 2019 that were saved before 19 October 2026 keep their 2019-based figure until your organisation's footprint is recalculated, which happens when you change a calculation setting or a site's country.
Why the year matters
The UK grid has changed a great deal. As an example, an office using 50,000 kWh of electricity a year produced 24.27 tonnes CO2e at the 2010 factor of 0.48531 kg per kWh, and 6.55 tonnes at the 2026 factor of 0.13096. Using one year's factor for another can make a footprint look much better or worse than it was. Our post on restating your baseline covers when a recalculation is needed and how to explain it.
