Once a business decides to start measuring its emissions, the bigger risk often shifts from “we never started” to “we started, but got it wrong in ways that quietly undermine the whole exercise.” Understanding the most common carbon accounting mistakes businesses make is the fastest way to avoid redoing months of work later, or worse, publishing a number that doesn’t hold up to scrutiny from investors, customers, or auditors.
None of these mistakes require specialist knowledge to fix — they are mostly process gaps that creep in when a business is moving fast and treating its first emissions inventory as a one-off project rather than a recurring discipline, as outlined in our beginner’s guide to carbon accounting.
Mistake 1: Leaving Out Scope 3 Entirely
The single most common gap is measuring only the emissions a business directly controls — its own fuel and electricity — while skipping everything in its wider value chain, like purchased goods, business travel, and waste. For most companies, this indirect category makes up the majority of their actual footprint. A carbon accounting exercise that stops at Scope 1 and 2 isn’t wrong, exactly, but it is dramatically incomplete, and reviewers increasingly notice when it’s missing.
Mistake 2: Double Counting Across Categories
Double counting happens when the same emissions get recorded twice — for example, counting a delivery van’s fuel under both the business’s own Scope 1 and again under a logistics partner’s reported Scope 3 figure if responsibility for that vehicle isn’t clearly assigned. It also shows up when teams independently track the same utility bill in two different spreadsheets. A simple fix is to assign one clear owner per emissions category and one single source spreadsheet that everyone references, rather than letting departments track figures independently.
Mistake 3: Using the Wrong or Outdated Emissions Factors
Emissions factors — the multipliers that convert a litre of fuel or a kilowatt-hour of electricity into an emissions figure — are updated periodically as grids change and measurement science improves. Businesses that copy a factor once and reuse it for years without checking for updates can end up with numbers that look precise but are quietly out of date. Always note the source and publication year of the emissions factors used, and review them at least once a year.
Mistake 4: Treating Poor Data Quality as a Reason to Skip a Category
When a category is hard to measure — supplier emissions are a frequent culprit — it’s tempting to leave it out entirely rather than report an imperfect estimate. This is backwards. A clearly labelled estimate, even a rough one based on industry averages, is more useful and more credible than a silent gap. Reviewers and auditors are generally far more forgiving of a transparent estimate than an unexplained omission.
Mistake 5: Not Keeping a Record of How Numbers Were Calculated
A figure with no audit trail is hard to defend and even harder to repeat next year. If the person who built the spreadsheet leaves the company, the entire calculation method can disappear with them. Keep a simple methodology note alongside every number: which emissions factor was used, where the activity data came from, and what was estimated versus measured. This single habit prevents most of the mistakes above from recurring silently year after year.
Avoiding these five mistakes won’t make a first carbon accounting exercise perfect, but it will make it credible — which matters more. Many sustainable changemakers profiled on Prakati built their early reporting habits by simply documenting what they didn’t know alongside what they did, the same discipline this checklist encourages. For a deeper look at the categories most prone to these errors, see our guide to carbon accounting and Scope 1, 2, and 3 emissions.