Guidance on year-on-year comparison

The Count Your Carbon calculator is updated annually to reflect improvements in data quality, emissions factors, and methodology. While these updates strengthen the accuracy and robustness of results, they also mean that direct year-on-year comparisons can sometimes be challenging.

Each year, certain questions may be amended, simplified, or removed based on stakeholder feedback and developments in carbon accounting best practice. Even minor changes in wording or calculation logic can result in small changes to a school’s, previously reported, carbon footprint.

Schools should therefore use results primarily to track overall trends and areas of high impact, rather than expecting identical comparability across different versions of the calculator.

The guidance below provides some additional context on the changes we’ve made for academic year 2025-26, to enable you to most accurately compare any future reports to those already completed.

Uniform

A specific area of change in Version 1.2 relates to how school uniforms are treated within the methodology:

In Version 1.1 (2024/25), uniform emissions were included in schools total carbon footprint. This approach was originally adopted to highlight the additional environmental impact of clothing purchased specifically for school use.

Following expert review, stakeholder feedback, and global carbon accounting guidelines, uniform has now been recognised as outside the operational boundary of the school.

Emissions from uniform purchasing technically sit with the individual or household, not the school. However, because some schools require specific uniform to be worn, the calculator continues to account for these emissions, but they are now reported separately from the school’s total footprint.

From Version 1.2 (2025/26) onwards, uniform emissions will no longer be included in a school’s total footprint. Instead, they will be reported separately as contextual information to support transparency.

Addition of Battery/Hybrid Electric Vehicles

Earlier versions of the calculator did not allow schools to report use of battery electric or hybrid vehicles.

From Version 1.2 (2025/26) onwards, these vehicle types can be selected, improving accuracy in transport-related emissions.

This change will generally result in a decrease in reported totals for schools that had previously recorded these vehicles as petrol or diesel vehicles, since electric and hybrid vehicle have lower associated emissions.

For schools that had previously excluded battery or hybrid vehicles altogether (due to the lack of an option), totals may increase slightly, as these journeys are now properly accounted for rather than omitted.

Staff and Student Commuting

Prior to December 2024, the calculator asked:
“In the last 12 months, what was the furthest distance, in miles, a student might travel to get to school?”

This was changed to:
“In the last 12 months, what was the average distance, in miles, a student might travel to get to school?”

The change impacted both student and staff commuting emissions, as the staff distance was previously estimated as 2x student distance.

In Version 1.2 (2025/26), the calculator now includes a specific question for staff commuting distance. This provides a more accurate estimate, as staff travel patterns often differ substantially depending on the school type, age group, or location.

Composting

In earlier versions of the calculator, schools were asked whether they composted food or garden waste on-site, and to estimate the proportion of waste managed in this way. However, these questions have now been removed in Version 1.2 (2025/26).

This decision was taken for two main reasons:

Confusion for users – Schools were uncertain how to record composting activity, particularly where food waste was collected by a contractor for industrial composting or anaerobic digestion. Some schools interpreted “on-site composting” as meaning zero bins collected, while others reported both bins and 100% composting. This led to inconsistent and unreliable data.

Negligible impact on results – The emissions associated with on-site composting are very small compared to other waste treatment routes. Furthermore, UK Government published emissions factors apply to industrial-scale composting, not small-scale school compost heaps, meaning that applying these factors would not give a representative result.

For these reasons, composting has been removed from the question set until a more robust and user-friendly approach can be implemented. Schools are still encouraged to compost as part of good environmental practice, but this is no longer included in the carbon footprint calculation.