Restating your baseline: when you must and how to explain it

Restate your carbon baseline when the business changes shape (an acquisition, a sale, outsourcing or insourcing), when you switch to a better method, or when you find a significant error, so you keep comparing like with like. Don't restate for growth, decline or the yearly change in government factors. Many firms treat a change of 5% or more of the baseline as significant.

Updated 16 October 2026 by the Carbon Recycling team. Figures use the official UK government conversion factors and are checked against the current gov.uk guidance.

Why restating matters

Your baseline is the yardstick for every reduction you claim. If the business changes shape and the yardstick doesn't, the comparison stops meaning anything. Buy another company and your emissions jump, though nothing got worse. Sell a division and they fall, though nothing got better. Restating puts the baseline on the same footing as today, so the trend shows real change.

When to restate, and when not to

What happened	Restate?
You bought a business that existed in your baseline year	Yes, add its baseline-year emissions
You sold or closed part of the business	Yes, take its baseline-year emissions out
You outsourced or brought in-house an activity, such as deliveries	Yes, if it moves emissions in or out of what you report
You switched to a better method or better data for a big source	Yes, recalculate the baseline the same way if you can
You found a significant mistake in the baseline	Yes, correct it
You grew, shrank, won or lost customers	No, that's real change
You opened a new site or bought a business that didn't exist in your baseline year	No, its emissions are new
The government's conversion factors changed	No, each year keeps its own factors

These are the triggers in the GHG Protocol's corporate standard, which the PPN 006 technical standard says your footprint should follow. Our post on why footprints fell with the 2026 factors explains the factor point in more detail.

Set a threshold before you need one

Small changes don't need a restatement, and restating every year makes your figures look unstable. Decide in advance what counts as significant and write it in your method note. A common choice is 5% of the baseline, for one change or several small ones added together. The GHG Protocol currently leaves the figure to each company, but its working groups have been discussing a set threshold, so check for changes when you next review your plan.

A worked example

A firm reported a 42 tonne baseline for 2023. In 2025 it buys a smaller competitor, which emitted 6.5 tonnes in 2023. Its 2025 footprint, including the new business, is 44 tonnes.

The acquisition is 15.5% of the original baseline, above the firm's 5% threshold, so it restates.
Restated 2023 baseline: 42 + 6.5 = 48.5 tonnes.
Against the old baseline, 2025 looks like a 4.8% increase. Against the restated one, it is a 9.3% reduction.

If the acquired firm's 2023 records aren't available, estimate them from its earliest full year you can evidence, and say so. Being open about the estimate is better than leaving it out.

Changing method

Better data is a common reason to restate. Say you counted purchased goods by spend in your baseline and now have supplier figures for your biggest lines. If you can apply the new method to the baseline year too, do. If you can't, because the old data no longer exists, keep the old baseline, and explain that part of the change comes from the method rather than from real reductions. Our post on purchased goods and services covers moving from spend to supplier data.

How to explain it

State the restated baseline and keep the original figure visible alongside it.
Say what changed, when, and how big the effect was, in one or two sentences.
Note your significance threshold and the method you used for any estimate.
Keep previous plans on your website. The PPN 006 standard says it is good practice, so evaluators can follow your progress.

PPN 006 asks you to review and update your plan every year, within six months of your financial year end, reflecting changes in your organisation's structure, so a restatement fits naturally into that update. Choosing the baseline in the first place is covered in how to pick a baseline year.

How Carbon Recycling helps

Carbon Recycling keeps each year's figures with the government factors for that year, and the Carbon Reduction Plan it builds has a baseline notes section where you explain a restatement in your own words.

Frequently asked questions

When should I recalculate my carbon baseline?

When something changes that would make the comparison unfair: buying or selling part of the business, moving an activity in or out of the company, a better calculation method, or finding a significant error. The GHG Protocol's corporate standard expects you to recalculate in those cases.

Should I recalculate my baseline when the government factors change?

No. A cleaner grid is a real change, so each year keeps its own year's factors. Recalculate for a factor change only if the old factor was wrong, or if you change method, for example from spend to supplier data.

What counts as a significant change?

You decide, and you should write it down. Many firms use 5% of the baseline. The GHG Protocol leaves the threshold to each company, though it is consulting on whether to set one.

Do I recalculate if we grow or shrink?

No. Winning more work, opening a new branch or losing customers changes your real emissions. That is exactly what the baseline is there to show, so leave it alone.

What do I put in my Carbon Reduction Plan?

Show the restated baseline, say what changed and why in a sentence or two, and keep the original figure visible. PPN 006 asks you to update your plan every year to reflect changes in your organisation's structure.

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