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What a CBAM certificate buffer costs to hold

Whether to hold a buffer and how big it should be are two different questions — and the first one does not depend on any of your own numbers.

An importer with 8,000 tonnes of goods a year, at an illustrative 1.8 tonnes of CO2e per tonne, owes 360 certificates for 2026 and pays €27,063 for them. That is €3.38 a tonne of product, which is the figure that makes a finance director stop reading. Two things follow from it, and only one of them is obvious.

The obvious one is that €3.38 a tonne does not stay €3.38 a tonne. The other is that the decision the number is usually cited to settle — whether to hold a buffer of certificates — cannot be settled by any of the importer’s own figures, because the answer is the same whatever they are.

What the phase-in does to the number

The CBAM factor rises from 2.5% in 2026 to 100 per cent in 2034, and the retained free allocation falls to meet it. Nothing else in the calculation moves.

YearCBAM factorCertificatesCost, €€ per tonne of product× 2026
20262.5%36027,0003.381.0
20275.0%72054,0006.752.0
202810.0%1,440108,00013.504.0
202922.5%3,240243,00030.389.0
203048.5%6,984523,80065.4719.4
203161.0%8,784658,80082.3524.4
203273.5%10,584793,80099.2229.4
203386.0%12,384928,800116.1034.4
2034100.0%14,4001,080,000135.0040.0
Same book of imports, same intensity, same €75 certificate price. Only the factor moves. 79.5% of the whole increase happens after 2029.

By 2030 — four years out, not eight — the same book of imports costs 19.4 times what it costs in 2026, and by 2034 40 times. The phase-in is also strongly back-loaded: 79.5% of the entire increase happens after 2029, which is exactly the interval a three-year plan does not reach.

2027, the year that pays twice

There is a second effect underneath the first, and it lands sooner. From 2027 the quarterly checkpoint requires the importer to hold 50% of the year-to-date obligation as it accrues — while the whole of the prior year’s obligation is still to be surrendered in September. So 2027 carries two obligations at once: €27,063 of lump sum for 2026, and €27,000 built up through the year for 2027.

Total: €54,063. An importer who budgets the 2026 lump sum and nothing else has provided for 50.1% of the year.

The factor of 2.00 is not a coincidence of these particular tonnages. The CBAM factor doubles between 2026 and 2027 — 2.5% to 5.0% — and the checkpoint is fifty per cent, so half of the 2027 obligation is arithmetically the whole of the 2026 one. Any importer, any volume, any intensity: the same two.

And it is not a one-year effect either. Every subsequent year carries the previous year’s whole obligation plus half of its own, with both terms growing.

YearSurrender for the prior yearIn-year build to 50%Total cash× prior year
202727,00027,00054,000
202854,00054,000108,0002.00
2029108,000121,500229,5002.12
2030243,000261,900504,9002.20
2031523,800329,400853,2001.69
2032658,800396,9001,055,7001.24
2033793,800464,4001,258,2001.19
Every year carries the previous year’s whole obligation plus half of its own, and both terms grow through the phase-in.

The cash requirement more than doubles again in 2028 and rises every year to 2033. That is the shape a treasury calendar has to hold, and it is a different shape from the annual cost line that most CBAM budgets contain.

The buffer: two questions, and only one of them is yours

The standard advice is to hold a buffer of certificates against the risk that verified supplier data arrives late or arrives worse than estimated, and to be careful because the repurchase entitlement is capped. Both halves deserve a number.

Take the cap first, because it is quickly disposed of. The repurchase entitlement is capped at the certificates the importer was obliged to buy — 360 here. A buffer only reaches that cap at a 100% buffer. Nothing in the plausible range comes close, so the cap is not the constraint. The 31 October repurchase deadline is.

Now the cost. A buffer bought in February and repurchased in October is 8 months of carry on its cost; what it protects against is the penalty on the certificates that would otherwise be missing. Both are proportional to the buffer.

BufferCertificatesCost, €Carry for 8 months, €Protection at risk, €Break-even P(shortfall)
5%181,350451,7552.56%
10%362,700903,5102.56%
15%544,0501355,2652.56%
20%725,4001807,0202.56%
30%1088,10027010,5302.56%
Six times the buffer, six times the carry, six times the protection — and the same number in the last column.

Read the last column down. The break-even is identical at every size. Carry and protection are both linear in the buffer, so the buffer cancels:

break-even P(shortfall) = r × m/12 ÷ k, with r the cost of capital, m the months carried and k the penalty as a multiple of the certificate price.

Which separates two questions that are usually asked as one. How big a buffer is a judgement about your own supplier data and nothing else can answer it. Whether to hold one is not a judgement at all — it has the same answer at five per cent and at thirty.

And the penalty figure the regulation will not give you

The obvious objection is that k is unknown: the penalty is indexed and pegged to the emissions-trading excess penalty, which is why a careful book declines to print a euro figure. It does not matter, because the answer is insensitive to it across the whole plausible range.

Penalty, as a multiple of the certificate priceBreak-even P(shortfall)
1.0×3.33%
1.3×2.56%
2.0×1.67%
3.0×1.11%
5.0×0.67%
The regulation indexes the penalty and the book declines to quote it, correctly. This table does not need the figure.

Between a penalty equal to the certificate price and one at five times it, the break-even probability moves from 0.67% to 3.33%. An importer relying on unverified supplier estimates is not below that, and knows it without any further analysis. The buffer decision is therefore made before the penalty is quantified — which is the only way it could be made at all, given that the penalty will not be quantified.

One trap in the arithmetic itself

Worth a paragraph because it runs in the direction that gets sanctioned. The surrender formula is often stated as several terms, one of which is a free-allocation adjustment, applied alongside the CBAM factor. But the factor and the retained free allocation are complements — 2.5% against 97.5% in 2026 — so the factor already carries the adjustment. A workbook built from the formula multiplies by an adjustment below one on top of a factor that contains it, and arrives at a smaller obligation than the schedule implies.

The implied adjustment in the worked figures here is exactly 1.00, which is the check to run. Counting it twice under-declares, and under-declaration is the direction the penalty regime exists to punish.

Three lines for the treasury paper

Budget 2027 at twice the 2026 lump sum, not at the 2026 lump sum, and hold the doubling as a rule rather than a forecast — it follows from the factor schedule and the fifty per cent checkpoint. Extend the plan past 2029, where 79% of the increase sits. And decide the buffer on the break-even rather than on its size: at any penalty between one and five times the price it sits under 3.3%, and no importer with unverified supplier data is below that.

The workbook behind this article

Every figure above is a live formula in the companion file for The CBAM Compliance Handbook, which reproduces the chapter’s worked example exactly, runs the phase-in to 2034, builds the 2027 payment calendar and sizes the buffer against the penalty it cannot quote. It is free, and it needs no account and no email address.

Open the companion file →

Also on this site

This note is drawn from The CBAM Compliance Handbook. The book is on Amazon.

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