Price Pulse · September 2026

Irish supermarkets reprice on a timetable. Thursday is when the cheapest shop changes.

Official food inflation is 0.1% a year. That did not stop a quarter of SuperValu's catalogue changing price on a single Thursday. Across 112 straight days and 5.5 million prices, every chain turns out to run its own clock, and on a Thursday the answer to "which supermarket is cheapest" changes about 68 times more often than on a Sunday.

This edition is built on every price we recorded from the retailers' own websites on 112 consecutive days, from 27 May to 15 September 2026: 5,522,336 price observations on 60,003 products across Aldi, Tesco, SuperValu and Dunnes. It is the first time we have had a long enough unbroken daily run to ask a question the monthly statistics cannot answer: not how much prices changed, but when. Every headline number below was recomputed from scratch by a second, independent piece of code, and every named product was re-fetched from the retailer's live customer page on the morning of publication.

A flat year is not a still shelf

The Central Statistics Office published its August figures on 10 September. Consumer prices were up 3.7% over the year, driven by energy, while food and non-alcoholic beverages were up 0.1% over the twelve months and down 0.1% in the month. On the official measure, Irish food prices have spent a year standing almost perfectly still.

Our shelf data does not contradict that. It complicates it. On Thursday 3 September, 26.3% of everything SuperValu sells online changed price in a single overnight step: 2,891 products out of 10,993. Three weeks earlier, on 13 August, it was 27.3%. Three weeks before that, 25.3%. A shopper standing in front of the shelf sees a quarter of the shop reprice at once, then almost nothing for twenty days, and the annual average of all that motion is roughly zero.

Inflation statistics measure the destination. This is a measurement of the journey, and the journey runs to a timetable.

Every chain has a price day

Take every pair of consecutive days for every product, ask whether the displayed price differs, and sort the answers by day of the week. The result is not noise. It is a schedule.

SuperValu is the sharpest clock in Irish grocery. On an average Thursday 8.40% of its products change price. On an average Saturday, 0.05%. That is a ratio of about 168 to 1 between the loudest day of its week and the quietest. Dunnes runs a day earlier and over two days, 2.32% on Tuesdays and 3.99% on Wednesdays. Aldi peaks on Thursday too, at 2.15%, though its cycle is the least regular of the four. Tesco has no weekly rhythm whatsoever: its busiest day, Sunday, moves 0.46% of products, and its quietest, Monday, 0.08%.

The retailers' own published offer windows say the same thing in their own words. Weighted by the number of products carrying them, 98% of SuperValu's offer windows start on a Thursday and 73% run exactly 21 days. Dunnes' windows start on a Wednesday 64% of the time and most commonly run 35 days (56%) or 28 days (21%). Tesco's start on a Wednesday 56% of the time and run 42 days in 44% of cases. Three chains, three different calendars, published openly on three websites.

The cycle is metronomic. SuperValu's five biggest repricing days in our window were 11 June, 2 July, 23 July, 13 August and 3 September: five Thursdays, each exactly 21 days after the last, each moving between 23.3% and 27.3% of the catalogue. You could have set a calendar reminder in June and predicted every one of them.

What actually moves on a Thursday

Here is where it pays to be careful, because "the price changed" hides a distinction the chains themselves do not handle the same way. When SuperValu or Dunnes put an item on offer, the offer price replaces the price on the product page. When Tesco runs a Clubcard deal, the shelf price stays where it is and a second, lower member price appears beside it. A raw count of price changes therefore flatters the chains that overwrite, and undersells the one that does not.

Decomposing SuperValu's 14,565 Thursday moves settles what they are. 6,592 are a product going on to an offer, 6,358 are a product coming off one, 1,037 move from one offer straight to another, and only 578 are a genuine shelf-price reset with no promotion at either end. The Thursday spike is, overwhelmingly, an offer cycle turning over: one set of roughly 6,500 deals expiring at midnight and another starting.

That is a real thing that happens to the price you pay. It is simply not the same thing as inflation, and the two are worth keeping apart. It is also why we publish shelf moves, promotions and loyalty prices as three separate signals rather than blending them into one number.

Tesco froze the shelf and moved the contest to the Clubcard

The most striking single number in this edition belongs to the chain with no clock. Of the 19,309 Tesco products we priced on at least 100 of the 112 days, 88.3% carried exactly one shelf price for the entire sixteen weeks. Not one change. At Dunnes the equivalent figure is 51.2%, at SuperValu 48.1%, at Aldi 54.3%.

That is not a chain declining to compete. It is a chain competing somewhere else. Run the same weekday analysis on Tesco's Clubcard price instead of its shelf price and the missing clock appears: 3.30% of Clubcard prices change on an average Tuesday and 1.82% on a Monday, against 0.16% on a Friday.

One product tells the whole story. Kellogg's Special K Original 750g sat at 6.90 euro at Tesco on every single one of the 112 days. Over the same period its Clubcard price took six different values: 3.45 euro, then no offer, then 5.50, then no offer, then 3.45 again, then 3.40, 3.20, 2.50, and from 8 September, 4.00 euro. The shelf price of that box has told you nothing useful since May. When we checked the live page on the morning of publication it was showing 4.00 euro with a Clubcard against a 6.90 euro shelf price.

It is the same story on Flahavan's More Than Oats Cocoa & Raspberry 400g (shelf 4.99 euro unchanged since May, Clubcard 4.00 from 30 June and 2.50 from 4 August, verified live at 2.50) and on Doritos Chilli Heatwave 140g (shelf 3.29 euro unchanged, verified live at 2.00 with a card). For a large part of the Tesco shop, the number on the shelf edge is a reference point rather than a price.

Which is why the cheapest shop changes on a Thursday

Now put the three calendars together. If SuperValu reprices a quarter of its range on Thursday, Dunnes reprices on Wednesday and Tesco holds still, then the ranking between them cannot be stable. We tested that directly.

Take every product identified by barcode as the identical item in at least three of the four chains: 4,862 products, giving 452,188 day-to-day comparisons. For each product on each day, work out which chain is cheapest on shelf prices, then ask how often that answer differs from the day before.

That instability is exactly why our cheapest-supermarket comparisons are always stamped with the week they were taken. Overall the cheapest chain changes on 2.68% of comparisons, but that average is close to meaningless: 8.82% of products change hands on a Thursday, 4.74% on a Wednesday and 4.32% on a Tuesday, against 0.13% on a Sunday, 0.25% on a Monday and 0.29% on a Friday. A price comparison you carried out on Monday is still almost perfectly accurate on Tuesday morning. By Thursday lunchtime it has gone stale on roughly one product in eleven.

We make no claim about why any chain picked the day it did, and what the data shows is chains on visibly different schedules rather than a shared one. We report the observed timing, and nothing about intent or conduct.

What a shopper can actually do with this

Start with what the data does not support, because the obvious inference is wrong. There is no cheap day of the week. The share of products carrying a promotion is almost perfectly flat: at Dunnes it sat between 44.2% and 44.4% on every day of the week, at Tesco between 37.1% and 37.4%. The weekly cycle changes which things are on offer, not how many. Shopping on a Thursday does not get you more deals, it gets you different ones.

What is genuinely usable is the expiry date, because it is predictable to the day. A SuperValu Real Rewards price starts on a Thursday at midnight and, three times in four, ends on the Wednesday night 21 days later. Birds Eye Chicken Burgers 8 pack are 5.00 euro at SuperValu at the time of writing, down from 10.50 euro, on a window that opened on Thursday 3 September and closes on Wednesday 23 September. A Dunnes offer runs longer, typically four or five weeks from a Wednesday: Dunnes Stores Irish Chicken Breast Fillets 440g at 5.99 euro on a buy-two-for-10-euro offer that started on Wednesday 19 August and ends on Tuesday 22 September, and Tofoo Naked Tofu 280g, reduced from 3.20 euro to 2.60 euro. All three prices were live on the retailers' own sites when we checked them on the morning of publication.

And at Tesco, treat the shelf price with caution. On 88.3% of the range it has not moved since the spring, while the price a cardholder actually pays turns over at the start of most weeks. If you compare Tesco against Dunnes or SuperValu on the shelf number alone, you are comparing two different kinds of object. You can check any product across all four chains for free.

A footnote: Aldi's prices end in 9, everybody else's end in 0

One more piece of structure is worth a paragraph, because it is obvious once you look. Ignoring alcohol, which has a legal price floor in Ireland under minimum unit pricing, 33.5% of Aldi's prices end in 99 cent and a further 14.9% end in 49: the classic discounter habit of stopping just short of a round number. At Tesco the distribution is close to the mirror image, 32.1% of prices ending in exactly 00 and 15.9% in 50. Dunnes (26.6% ending in 00) and SuperValu (17.1%) sit in between, both keeping a real tail of 99s. Two chains, two opposite theories of what a price should look like, applied across tens of thousands of products.

It also sits alongside the other structural gap we measured in August, when own label came out 49% cheaper per kilo or litre than the brand beside it. For context on how unusual any of this movement is, the European Central Bank's Inflation Persistence Network found that euro-area consumer prices covered by the CPI are "unchanged on average for 4 to 5 quarters", with around 40% of changes being reductions. Our Tesco shelf figure, 88.3% unchanged across not quite four months, sits comfortably inside that picture. SuperValu's Thursday does not, and the reason is that most of what moves there is a promotion rather than a list price.

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