What the data actually shows
The core idea is the left-digit effect: because we encode prices from the left, changing the leftmost digit ($9.99 versus $10.00) has an outsized effect on perceived magnitude compared with changing a rightmost digit ($9.98 versus $9.99). Work by Thomas and Morwitz on this effect found that the drop from $3.00 to $2.99 felt larger to people than the same one-cent drop from $3.49 to $3.48, because only the first crosses a digit boundary.
Prices ending in 9 are also strikingly common and have been linked in research on charm and psychological pricing to higher perceived value and, in some field studies, higher sales — though effects vary by product, category, and context rather than being uniform. The 9-ending has additionally become a learned cue for 'this is a deal,' which can lift demand independently of the small price reduction itself.
It is worth being careful here: the size of these effects is debated and not universal. Some studies find meaningful sales bumps, others find little or context-dependent results, and the cue can even backfire for premium goods, where round numbers can signal quality. The reliable, well-supported part is the underlying perceptual mechanism — left-to-right reading and first-digit anchoring — not a guaranteed sales lift in every case.
Why this feels different from how it actually is
It feels like you are evaluating the whole price, but in practice attention is front-loaded onto the first digit or two, especially when you are scanning quickly. That first glance sets an anchor — 'nine dollars' — and the cents that follow get rounded down in your mind rather than up. The result is a price that feels meaningfully cheaper than the round number a penny above it.
The 'value' association does its own quiet work. Years of seeing sale tags and discount prices end in 9 have trained most shoppers to read a 9-ending as a signal of a bargain, so the number can feel like a deal even when it is simply the everyday price. You are responding to a learned cue as much as to the actual figure.
And the stakes per item feel trivial — it is only a penny — so it rarely seems worth scrutinising. But the technique is applied across nearly everything you buy, repeatedly, which is exactly why a one-cent gap is worth a seller's effort even if it is not worth your worry on any single purchase.
The actual saving is one cent. The difference is entirely in perception.
What the research says to do about it
The simplest research-aligned move is to round prices up in your head before deciding: read $9.99 as $10, $19.99 as $20. Mentally crossing the boundary the price was designed to avoid neutralises most of the left-digit effect, because you are restoring the magnitude your quick glance shaved off.
Compare on unit price and total, not on the headline figure. Shelf unit pricing (cost per ounce, per item) sidesteps charm pricing entirely, and looking at the full basket total rather than individual sticker prices makes the cumulative effect of many just-below prices visible.
More broadly, the useful habit is to treat a 9-ending as a neutral price, not as evidence of a deal. A price ending in 9 tells you almost nothing about whether something is actually discounted; checking the regular price or price history is what separates a real saving from a learned association.
What the research says does not help
Assuming you are immune because you 'know the trick' does not reliably help. The left-digit effect operates fast and largely below deliberate attention, so awareness reduces but does not switch it off — which is why the round-up-in-your-head habit matters more than simply knowing the effect exists.
Treating a 9-ending as proof of a bargain is the opposite of helpful. The ending is a pricing convention, not a discount; many full-price items end in 9, so reading it as a saving is exactly the association the practice relies on.
Obsessing over the single penny misses the point and the scale. The difference on any one item is genuinely tiny; the thing worth attention is that the same nudge is applied to almost every price you see, so the defence is a consistent habit of rounding and comparing, not anxiety over individual cents.
A price ending in 9 tells you almost nothing about whether something is actually discounted.
What this looks like in real life
The glance that rounds down
Scanning a shelf quickly, your attention front-loads onto the first digit or two. That first glance sets an anchor — 'nine dollars' — and the cents that follow get rounded down in your mind rather than up. The result is a price that feels meaningfully cheaper than the round number a penny above it.
Reading $9.99 as $10
The simplest research-aligned habit is to mentally cross the boundary the price was built to avoid: read $9.99 as $10 and $19.99 as $20. That restores the magnitude your quick glance shaved off — and because the effect runs fast and below deliberate attention, the habit matters more than simply knowing the trick exists.
Real numbers in context
The mechanism is about a digit, not a dollar. In Thomas and Morwitz's work on the left-digit effect, a drop from $3.00 to $2.99 was perceived as a larger reduction than the same one-cent drop from $3.49 to $3.48, because only the first changes the leftmost digit. The actual saving in both cases is one cent — the difference is entirely in perception.
Prices ending in 9 are extremely common across retail, and research on charm pricing has linked them to higher perceived value and, in some field experiments, higher sales — but the effects are uneven across products and contexts, and round-number pricing can signal quality for premium goods. Treat 'prices ending in 9 boost sales' as a real but context-dependent finding, not a universal law, while the underlying left-to-right, first-digit anchoring is the well-supported core.
In Thomas and Morwitz's work, the identical one-cent reduction felt larger when it crossed the leftmost digit than when it didn't. The saving is a penny in both rows — the difference is entirely in perception.
| Price drop | Amount saved | Crosses the left digit? |
|---|---|---|
| $3.00 → $2.99 | 1¢ | Yes — felt larger |
| $3.49 → $3.48 | 1¢ | No — felt smaller |