The Best Carbon Accounting Software for Mid-Sized and Large Corporates

When was the last time you invited a software into the audit meeting? This is what the team here at Sumday are use to.

We support our clients from implementation through to sitting in the room with the auditor as they often learn how to audit GHG Inventories. The Sumday team of ex-auditors, both financial and ESG from the big four can speak the language of auditors in a way other platforms talk about foreign lines of code.

If you're a mid-sized or large organisation searching for carbon accounting software, chances are you're not looking for a shiny ESG dashboard or a one-off emissions calculator. You're looking for something that your finance team trusts, your auditors won't tear apart, your sustainability team can actually use, and your board feels confident signing off on.

Carbon Accounting Has Changed (And the Tools Need to Catch Up)

Carbon accounting used to sit on the edges of the business. A spreadsheet. A consultant once a year. A report no one really wanted to own. That's no longer the world we're in.

With ASRS S2, IFRS S2, and increasing audit scrutiny, carbon data is now treated much more like financial data. And that's where a lot of "ESG tools" start to fall over. Carbon accounting isn't just sustainability anymore, it's accounting.

Built by an Ex-PwC Auditor (And It Shows)

Different to other platforms in market Sumday was built by an ex-PwC auditor who had seen firsthand how carbon reporting breaks down under real audit conditions. So instead of building a tool for storytelling, Sumday was built for finance teams, sustainability teams working with finance, risk and compliance teams, and external auditors.

Why Mid-Sized and Large Businesses Choose Sumday

1. It Starts With Your Financial Data

Most Scope 3 emissions live in your general ledger, not in surveys or estimates. Sumday starts there. You import your actual financial transactions, and emissions are calculated from real spend and activity data.

2. Audit-Ready Carbon Accounting

Every emissions number in Sumday can be traced back to the source transaction, the methodology used, the emission factor applied, and the assumptions made. You can leave notes, attach documents, and export carbon working papers in a format auditors actually understand.

3. Designed for Complex Organisations

Sumday is purpose-built for mid-sized and large organisations, including those with multiple entities or brands, distributed teams, complex supply chains, and heavy Scope 3 exposure.

4. Scope 3 Without the Pain

Sumday takes a very practical approach: start with spend-based data, improve quality over time, engage suppliers directly in the platform, give suppliers free access, education and support, and replace averages with real data as it becomes available.

5. Built-In Education

Every customer gets access to the Sumday Academy, practical training used by accountants and auditors, an accounting support help desk staffed by ex-auditors, and embedded AI that explains decisions, not just outputs.

Enterprise-Grade Security, Without the Drama

Sumday is hosted on Microsoft Azure and meets the security expectations of large organisations, including Single Sign-On (SSO), Multi-Factor Authentication (MFA), encryption at rest and in transit, full audit logging, and data residency options.

Who Sumday Is Best For

Sumday is a strong fit if you're a mid-sized or large business, preparing for NGERs, ASRS S2 / IFRS S2, working with external auditors, looking to embed carbon accounting into finance processes, and ready to move beyond spreadsheets and basic ESG tools.