A price of 10,000 won looks like a ten-thousand-won purchase. Change it to 9,900 won, and it can feel as if it still belongs below that level. The real difference is only 100 won.
The familiar English-language comparison is $9.99 versus $10. We can do the subtraction. The interesting part is the impression that arrives before we stop to calculate.
Crossing a digit boundary
Prices just below and at a round amount sit on opposite sides of a prominent digit boundary. That can make the apparent gap feel larger than the numerical difference.
Researchers call the influence of leftmost digits on price judgments the left-digit bias. A 2020 consumer study explored when it occurs.
This does not mean people literally calculate 9,900 as 9,000. You can know the exact amount while your immediate impression of its size is influenced by how the digits look.
The price beside it matters too
The study compared judgments made with prices visible side by side against judgments involving a price recalled from memory. The bias tended to be stronger in the direct visual comparisons.
A practical way to apply that insight is to calculate the actual saving when a crossed-out old price sits beside a new one. A striking layout does not necessarily mean a large discount.
A reduction from 10,000 won to 9,900 won is 1%. From $10 to $9.99, it is 0.1%. Those are separate examples, not currency conversions. Looking at the amount saved helps separate impression from arithmetic.
Is nine a magic sales ingredient?
No. MIT's profile of pricing research describes how nine-ending prices and sale cues can work differently depending on their use.
An analysis hosted by MIT also found a weaker effect when nine endings were highly prevalent. Each study has its own setting; neither provides a universal formula for selling every product.
Quality and usefulness still matter. Paying a little more for a shirt you will wear can be better than paying less for one that stays in the wardrobe. The last digit cannot answer all the important questions.
Small differences can add up
For ten identical hypothetical items, 9,900 won each totals 99,000 won, compared with 100,000 won at 10,000 each. The difference is exactly 1,000 won. A small per-item saving need not be ignored.
On the other hand, delivery charges, quantity and package size can change the total. Compare different-sized products by unit price. The aim is to put both offers on the same basis.
A simple way to reread a price tag
Let the first impression happen, then add one calculation. Use a rounded estimate for your budget and check the precise saving, quantity and final total before buying.
Also ask whether you would want the product without the price tag. Is it something you needed? Do you already have an equivalent? Saving 100 won on an unnecessary 9,900-won purchase still means spending 9,900 won.
So why choose a price ending in nine?
It can slightly reduce the actual price while creating the impression of a lower price level. A digit boundary can influence that impression. But a nine ending does not automatically make an offer cheap or deceive every shopper. Make the decision with the actual saving and total cost.