Best Carbon Accounting Software (2026): 10 Tools

Most small businesses start measuring carbon for one reason: a big customer sent a supplier questionnaire and wants numbers by the end of the quarter. That's a stressful way to begin, and it's why the right tool matters more than the most impressive one.

This list covers carbon accounting, product footprint and sustainability reporting software. If you're looking for quick wins first, my guide to sustainability upgrades that save a small business money is a good start, and so is this piece on how going green can help your bottom line.

Carbon accounting software compared

Here's what each tool is, what it's good for and whether its own site names a free plan, a trial or neither. The list is alphabetical and in no particular order.

Tool	Type	Good for	Free plan
Altruistiq	Food and drink	Food and beverage footprints	No
Carbon Trail	Fashion and retail	Product impact with supplier data	No
Greenly	Carbon management	SMEs starting to measure	No
Normative	Audit-ready accounting	Verified scope 1 to 3 numbers	No
Persefoni	Carbon accounting	Free footprint to start	Yes
Plan A	Decarbonisation	Reduction plans, not just reports	No
Sumday	Procurement and carbon	Supply chain emissions	No
Sweep	ESG reporting	One dataset for many frameworks	No
Watershed	Enterprise sustainability	Large companies with complex footprints	No
Zevero	Expert-led carbon	Growing businesses wanting guidance	No

Carbon accounting and sustainability platforms

Altruistiq

Best for: Food and drink brands that need product and farm-level emissions, not just office electricity and travel.

Carbon Trail

Best for: Fashion and retail brands measuring product impact from primary supplier data for reporting and product passports.

Greenly

Best for: Small and mid-sized companies measuring their footprint for the first time who want help as well as software.

Normative

Best for: Companies that expect auditors or big customers to check their numbers and want everything built to the GHG Protocol.

Persefoni

Best for: Smaller firms answering their first customer questionnaire who want a free place to calculate a footprint.

Plan A

Best for: Businesses that want to move from measuring to cutting emissions, with reduction targets and supplier engagement.

Sumday

Best for: Organisations whose biggest emissions sit in what they buy, so procurement and carbon need to be looked at together.

Sweep

Best for: Teams reporting to several frameworks at once who want to upload data once and reuse it across every report.

Watershed

Best for: Large companies with complicated supply chains and investor-grade reporting needs across many countries and business units.

Zevero

Best for: Growing businesses that win deals on carbon data and want experts reviewing their numbers alongside the software.

Scope 1, 2 and 3 in plain English

• Scope 1: emissions you make directly, like gas boilers and company vehicles.
• Scope 2: emissions from the electricity and heat you buy.
• Scope 3: everything else in your value chain, from what you buy to how customers use your products. For many businesses, it's the biggest part.

Who has to report in the UK

GOV.UK's environmental reporting guidelines are designed to help companies and limited liability partnerships comply with the Streamlined Energy and Carbon Reporting regulations. The page also records that all UK quoted companies have had to report their greenhouse gas emissions since 2013.

If you're a small business, SECR probably doesn't apply to you directly. Your larger customers may well be reporting, though, and their scope 3 includes what they buy from you. That's why supplier questionnaires are landing in small business inboxes.

What to gather before you start

1. Twelve months of electricity and gas bills, or meter readings.
2. Fuel use or mileage for company vehicles.
3. Business travel, from flights and trains to hotel nights.
4. Your spend by supplier category, from your accounts.
5. Any product or supplier data your customers have asked about.

Questions to ask before you buy

• Which reporting frameworks does it support, and which do you need?
• Does it calculate from spend data, activity data or both?
• Will an expert review your numbers, or is it self-serve?
• Can you export a report your customers will accept?
• How does it help you plan reductions, not just measure?

A footprint that sits in a dashboard does nothing. The tools worth paying for help you decide what to change next.

Answering a supplier questionnaire

When a big customer asks for your carbon data, read the questionnaire carefully before you start. Some only want a total footprint, some want it split by scope and a few want product-level numbers. Answer what's asked, explain the method you used in a sentence and say what you'll improve over the coming months.

Don't guess or round numbers to look better. A clear, honest first footprint with a plan to reduce it reads far better to a procurement team than suspiciously perfect data. Keep a copy of every answer you send, because the same customer will usually ask again a year later, and they'll compare.

If you sell to several large companies, you'll often find they ask similar questions in different formats. A tool that stores your data once and exports it in several ways will save you a lot of evenings.

Do you make carbon accounting software? Tool makers can ask to be considered for a featured place on this list.

My advice on carbon accounting software

If a customer questionnaire started this, begin with a tool that has a free option or plenty of guidance, and get a reasonable first footprint rather than a perfect one. You can tighten the numbers each year.

If investors, auditors or big contracts depend on your data, choose a platform with verified methods and expert review from the start. Redoing a year of carbon accounts is a miserable job.

Frequently asked questions

What is carbon accounting software?

It's software that calculates your greenhouse gas emissions from energy, travel, purchases and supplier data, then helps you report and reduce them.

Do small businesses need carbon accounting?

Not always by law, but larger customers increasingly ask their suppliers for emissions data. A simple footprint helps you answer those questions and win work.

What is SECR?

Streamlined Energy and Carbon Reporting is a UK reporting requirement. GOV.UK publishes environmental reporting guidelines to help companies and LLPs comply with it.

What are scope 3 emissions?

They're the indirect emissions in your value chain, such as the goods and services you buy and how your products are used. For many businesses they're the largest share.

Is there free carbon accounting software?

A few platforms offer a free carbon accounting tier to get you started, with upgrades for advanced reporting.