Quick answer: €9.99 feels cheaper than €10 because of the left-digit effect: your brain forms an impression of a price from its first digit, so €9.99 gets filed as "nine-something." Retailers call it charm pricing. Rounding every price up in your head, especially on busy sale days, shows you the real cost.
Part of our complete guide: Why Do I Spend Money? The Psychology of Spending, Explained.
You know €9.99 is basically €10. Everyone knows. And yet, somewhere in your brain, €9.99 still feels like "about nine euros". Before Black Friday, when nearly every price will end in .99, it is worth understanding why — because this tiny trick is one of the most studied effects in consumer psychology.
What does the research say about prices ending in 9?
Field studies show 9-endings really change behaviour. In one experiment a dress sold better at $39 than at a cheaper $34, and in 22 million used-car sales, cars just under a round mileage sold for noticeably more.
The $39 dress that beat a cheaper price
Marketing professors Eric Anderson (Northwestern) and Duncan Simester (MIT) ran field experiments with a real mail-order clothing retailer, published in Quantitative Marketing and Economics in 2003. They sent catalogues where the same dress had different prices. The result most often cited from their work: the dress sold 21 units at $39 — more than at $34 (16 units) and more than at $44 (17 units). A higher price ending in 9 outsold a cheaper one. Across their experiments, 9-endings increased demand, especially for new items.
22 million used cars can't be wrong
Economists Nicola Lacetera, Devin Pope and Justin Sydnor analysed more than 22 million used-car sales (published in the American Economic Review, 2012). They found sharp drops in price every time the mileage crossed a round 10,000-mile mark. A car with 79,900 miles sold for roughly $200 more than an almost identical car with 80,000 miles — even though 100 miles makes almost no real difference. Buyers were anchoring on the first digit.
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Why does my brain only read the first digit?
We read from left to right, and our brains are efficient — sometimes too efficient. When we see a price, we start forming an impression of its size from the very first digit, before we have finished reading. In €9.99, the "9" sets the impression: nine-something. The cents arrive too late to fully correct it. Researchers call this the left-digit effect, and retailers call it charm pricing.
It is strongest when we are rushing, distracted or comparing many prices quickly — which is exactly what Black Friday and holiday shopping feel like.
How do I see the real price?
- Round up, always. Train yourself to read €49.99 as €50 and €199 as €200. Say the rounded number in your head.
- Compare in whole numbers. When choosing between options, write both prices rounded up. The "bargain" often disappears.
- Watch the thresholds. Prices like €99, €199 and €999 are designed to stay just below a mental line. Ask: would I pay €100 for this?
- Slow down on sale days. The effect grows when you are in a hurry. Decide your Black Friday list and budget the day before. (See Black Friday 2026 budget plan.)
- Track in round numbers. In your budget or money diary, round every purchase up. You will see your spending more honestly — and often save the difference.
Do your workbooks use .99 pricing too?
Yes — our own workbooks end in .99 too. The Money Brain Workbook is €14.99, which is really €15. The complete 3-step bundle is €49.99, which is really €50. We would rather you buy it knowing exactly what you are paying, because that is what this whole journal is about: seeing your money clearly and choosing on purpose.
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FAQ
What is the left-digit effect?
It's the tendency to judge a number mainly by its first digit, so €9.99 feels much closer to €9 than to €10.
Why do stores use .99 prices?
Because research shows prices just below a round number can increase sales, even when the difference is only one cent.
How do I avoid falling for charm pricing?
Round every price up before comparing, set a budget before sale days, and ask whether you'd pay the rounded amount.
Keep reading:
- Why Do I Spend Money? The Psychology of Spending
- How scarcity marketing creates urgency
- Girl math explained
Sources
- Anderson, E. T. & Simester, D. I. (2003). Effects of $9 price endings on retail sales: Evidence from field experiments. Quantitative Marketing and Economics, 1, 93–110.
- Lacetera, N., Pope, D. G. & Sydnor, J. R. (2012). Heuristic thinking and limited attention in the car market. American Economic Review, 102(5). Working paper: NBER.