The window for IFRS 18 comparatives is open. Most groups have not started.

Most UK groups treating IFRS 18 as a 2027 problem are already eight months behind. The standard is effective for annual periods beginning 1 January 2027. For a December year-end, that means the comparative period being reported in the first IFRS 18 financial statements is the year currently in flight. Every transaction posted into 2026 ledgers is comparative data for the 2027 financials, whether the finance function has acknowledged that or not.

The substantive work is not the policy paper. The substantive work is the chart of accounts. IFRS 18 introduces three statutory categories on the income statement, operating, investing, and financing, and the accounts have to map cleanly into them, item by item, with management-defined performance measures reconciled formally to the IFRS subtotals. A group running a flat trial balance with categories that emerged organically over a decade does not have that mapping. The mapping is a six-to-twelve-week piece of work for a mid-cap, and the moment to do it is during the comparative year, not during the year of first application.

The other piece that gets underestimated is the management-defined performance measure reconciliation. Adjusted EBITDA, normalised operating profit, underlying earnings: every one of these now lives inside the financial statements rather than in the front-half narrative, with a reconciliation that the audit firm signs off as part of the audit opinion. APMs that have drifted from one year to the next without a written definition are about to find that they need one.

The disaggregation requirement is the third trap. IFRS 18 demands separate presentation of material expense components inside operating profit, and the materiality test is sharper than most groups are used to applying at line-item level. A discretionary marketing budget that has historically sat inside "operating expenses" may now need to be presented as its own line on the face of the income statement. The judgements should be made now, not in a partner review during the FY27 audit cycle.

The reason most groups have not started is not technical. It is that the audit firm has not raised the alarm yet, the board has not asked the question yet, and the finance team is fully occupied with the close cycle in front of them. The standards transition becomes urgent at the point where it is no longer comfortable to be early.

The work that lands the buyer in a defensible position by end of December 2026 is a chart-of-accounts mapping, an MDPM register, a disaggregation register, and a transition memo. None of it is heroic. All of it has to happen in the next twenty-four weeks.

The senior register of practitioners who have actually built these reconciliations on live engagements is small. Atlas Verum runs the work alongside the existing finance team, on retainer or programme, with documentation built to inspection standard from the first paper. Where the client wants the audit firm in the room early, we coordinate it. Where the client wants to land the file cleanly before the partner sees it, we land it.

The choice is not whether to do this work. The choice is whether it gets done deliberately, between May and December, by a senior hand who has done it before, or whether it gets done in panic mode during the FY27 audit, when the time to be deliberate has passed.

The window is open.