Building a like for like event comparison when the portfolio changed shape

The portfolio review says revenue is up 11.2 per cent. Halfway down the room, a show director says her show is basically flat and so is the one next to her, and she wants to know where the 11.2 per cent came from.

She is right, and the pack is right, and what is missing is a like for like event comparison that names which editions are in the measurement and which are not. That list is the whole exercise. Once you have it the arithmetic takes five minutes.

What does like for like mean for a portfolio of shows?

An edition present in both periods, under the same ownership, running its normal cycle. Everything else comes out of both sides of the comparison.

The four exclusions are the ones a corporate finance team would recognise and one extra that belongs to event businesses specifically.

Launches. A show in its first edition has no comparative, so it cannot be in a like for like set. It should absolutely be in the group's growth story, which is a different measure and worth keeping separate.

Acquisitions. An acquired show joins the set once both periods contain an edition of it under group ownership. Before that, including it measures the purchase.

Disposals and closures. These come out of the comparative, which is where teams go wrong, and the section below works through why.

Cycling shows. A biennial that ran last year and does not run this year has to leave the set for the year it is absent, or return to it against the right comparative. That correction is enough of a topic on its own that the biennial cycling adjustment is where the detail sits.

The arithmetic on eleven shows

The portfolio runs eleven shows this year and reported 38.8 million of revenue. Last year it ran nine and reported 34.9 million. Reported growth is 3.9 million on 34.9 million, which is 11.2 per cent.

Three of this year's eleven were not in last year's nine. Two are launches, contributing 1.2 million between them. One was acquired in February this year and contributed 4.0 million.

Last year's nine included a show sold in December, which contributed 2.4 million to that year and nothing to this one.

That leaves eight editions present in both periods. They produced 33.6 million this year against 32.5 million last year, so like for like growth is 1.1 million on 32.5 million, which is 3.4 per cent.

Eleven point two per cent at the top, 3.4 per cent underneath it, and a 7.8 point gap made entirely of portfolio shape. The show director in the meeting was describing the second number accurately.

Why does the base matter more than the numerator?

Because most teams remember to take the new shows out of the current year and forget to take the sold show out of the comparative, and the second omission is larger than the first.

Run the wrong version on the same portfolio. Strip the 1.2 million of launches and the 4.0 million acquisition out of this year, giving 33.6 million, and compare it against the full 34.9 million the group reported last year. That produces a decline of 1.3 million, or 3.7 per cent.

The same eight shows now read as growing 3.4 per cent or shrinking 3.7 per cent, a swing of 7.1 percentage points, decided by whether one line was removed from the base. Nobody in that chain did anything dishonest. The current year got cleaned because the new shows were obvious, and the comparative got left alone because the sold show was somebody else's problem by then.

Informa PLC describes the correct treatment in the glossary of its 2025 full year results. Acquisitions are "included on a pro-forma basis from the first day of ownership in the comparative period", and disposals are "similarly adjusted for on a pro-forma basis to exclude results in the comparative period from the date of disposal". Both sides get the same surgery, which is the entire point.

What a published version looks like

Informa's 2025 statement reported revenue of 4,041.4 million pounds against 3,553.1 million in 2024, growth of 13.7 per cent. Underneath that it published a four column bridge from underlying growth to reported growth: underlying 6.3 per cent, phasing and other items 1.3 per cent, acquisitions and disposals 8.0 per cent, and currency change negative 1.9 per cent.

Two things are worth taking from that table. The acquisitions and disposals column is larger than the underlying column, which is normal for a group that has been buying, and it is presented as its own line rather than folded into anything else. And the phasing column swings sign between years, at positive 1.3 per cent in 2025 against negative 3.4 per cent in 2024, which tells you how much of a single year's reported growth can be scheduling.

At organiser scale the same table has four columns and one row per show, and it is the single most useful page in a portfolio review. It answers the show director's question before she asks it.

Naming the set, and keeping it named

The part that decays is the list itself.

Store the like for like set as an explicit list of edition identifiers for each comparison, saved with the report, rather than deriving it at run time from a rule. Rules look cleaner and drift, because somebody changes a show's status field in the events table for an unrelated reason and last quarter's like for like number quietly changes with it.

Keep the set stable within a reporting year. If a show is disposed of in month nine, the like for like set used for the full year should be the one that excludes it, and the interim reports issued before the sale will not match. Say so in a footnote rather than restating three published packs.

Two versions are worth publishing side by side when the portfolio has moved a lot: the strict set, which is only editions in both periods, and the total, which is everything. The gap between them is a real management number, because it says how much of the year's growth was bought or built rather than traded. The group level version of that split has its own conventions, which is where an organic growth definition does its work.

Where this stops

A like for like comparison assumes an edition is comparable to itself, and sometimes it is not.

A show that moved from a 22,000 square metre hall to a 31,000 square metre hall is in the set, and it will show strong growth that has more to do with the venue than with the commercial team. A show that changed from two days to three is in the set. A show that merged with another show in the portfolio has genuinely stopped being comparable, and the honest treatment is to remove both from the set and say why.

The set also shrinks in exactly the years you want it most. A group that made four acquisitions and two disposals in one year might have a like for like set covering under half its revenue, and a 3.4 per cent growth rate measured on 40 per cent of the business is a weak claim about the whole. Publish the coverage percentage next to the growth rate and let the reader weigh it.

There is a final trap in the vocabulary. The same phrase gets used for pacing claims about contracted revenue for shows that have not happened yet, which is a different measurement with its own comparison date problem. Using one term for both invites somebody to compare them.

The first step this week

List every edition that ran in each of the last two years, side by side, and mark each row as in or out of the set with a one word reason. Total the in rows for both years and divide. If that number differs from the growth rate in your last board pack by more than a point, the pack has been comparing portfolios of different shapes, and the fix is the list rather than the formula. File it with the rest of the finance reporting definitions so next quarter starts from it.