Left-digit effect
The left-digit effect is the tendency to judge a number mostly by its leftmost digit, so a price just below a round number feels noticeably smaller than it is.
People read numbers from left to right and start judging before they reach the end. Thomas and Morwitz showed that a nine-ending price like $2.99 is judged meaningfully lower than $3.00, but mainly when the one-cent drop changes the leftmost digit. The effect holds in real markets with large sums: across more than 22 million wholesale used-car sales, prices dropped sharply each time the odometer crossed a 10,000-mile mark. It also shifts choices between options. When two gifts were priced $29.99 and $39.99, only 25% of people picked the more expensive one; with round prices, twice as many did. In three field experiments with a retailer, $9 price endings increased demand, most of all for new items and less when items were also marked as on sale. Charm prices are not always better, though. For purchases driven by feelings, round prices feel right and are rated more favorably.
How to apply
- Price just below a round number when it changes the leftmost digit: 49 instead of 50, 1,990 instead of 2,000. Changing 47 to 46.99 does little.
- To steer people toward a higher tier, use round prices for both. Just-below prices make the gap look bigger and push people to the cheaper option.
- Use charm prices on new products, where customers have no price history to compare against. That is where $9 endings helped most.
- Use round prices for gifts, experiences and other purchases people decide on by feel.
What to avoid
- Putting .99 on everything. The effect works mainly when the leftmost digit changes, and it weakens when combined with sale signals.
- Keeping the headline price under a threshold by moving mandatory costs to later steps. People judge the total, and in the EU, displayed prices must already include taxes.
- Just-below prices on a premium or emotional purchase where a round number would feel more fitting.
Real-world examples
References
- Thomas & Morwitz (2005). Penny Wise and Pound Foolish: The Left-Digit Effect in Price Cognition. Journal of Consumer Research.
- Lacetera, Pope & Sydnor (2012). Heuristic Thinking and Limited Attention in the Car Market. American Economic Review.
- Manning & Sprott (2009). Price Endings, Left-Digit Effects, and Choice. Journal of Consumer Research.
- Anderson & Simester (2003). Effects of $9 Price Endings on Retail Sales: Evidence from Field Experiments. Quantitative Marketing and Economics.
- Wadhwa & Zhang (2015). This Number Just Feels Right: The Impact of Roundedness of Price Numbers on Product Evaluations. Journal of Consumer Research.
For agents
An agent-friendly guide to this principle lives at /agents/left-digit-effect.md.
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Similar principles
Disclaimer: The theories here are just that — theories. They may not apply universally and should be considered in context. Use your own judgment and consult additional sources when applying these principles.