Weber-Fechner's Law on a landing page: what price discount a visitor actually notices

A €10 discount shown on a landing page lands completely differently depending on the starting price: on a €20 ebook, it jumps out and triggers the purchase; on a €300 service, the same absolute amount barely registers. That isn't a matter of perceived generosity or layout — it's a psychophysics result measured for nearly two centuries, known as Weber-Fechner's Law. This guide explains exactly what it says about a perception threshold, how it overlaps with (and sharpens) the strikethrough-price rule most e-commerce sellers already know, and how to size a discount, a pricing table, or an order bump so it's actually seen.

Weber-Fechner's Law, in one sentence

In the 1830s, German physiologist Ernst Heinrich Weber showed that a person doesn't perceive the difference between two stimuli (a weight, a brightness, a sound) in absolute terms, but as a proportion of the starting stimulus: the larger the initial stimulus already is, the larger the absolute change needed for it to become "just noticeable." Psychophysicist Gustav Fechner formalized that result in 1860 in his foundational book Elemente der Psychophysik (see on Google Scholar), showing that the perceived intensity of a stimulus grows logarithmically with its actual physical intensity: past a certain point, each additional unit added to an already-large stimulus is noticed less and less. Applied to a price, the principle translates as follows: what determines how a discount is perceived isn't the amount subtracted, but its ratio to the starting price.

The differential threshold, or why the percentage matters more than the amount

In marketing, this minimum proportion needed for a price change to be noticed has a precise name: the differential threshold, or just noticeable difference (JND). The reference study on its application to price is Kent B. Monroe's, "Measuring Price Thresholds by Psychophysics and Latitudes of Acceptance," published in 1971 in the Journal of Marketing Research. Monroe shows that buyers hold a tolerance zone around a price they perceive as normal, and that the threshold beyond which a price change becomes noticeable follows Weber-Fechner's proportional logic rather than a fixed threshold in currency. In practice: a discount perceived as significant typically falls between 15 and 20% of the listed price, whatever that price is — €3 off a €15 item, or €45 off a €300 item, produce a comparable perceived effect, even though their absolute amounts have nothing in common.

Where this actually changes a landing page

• The strikethrough price — a discount displayed below the proportional threshold ("-€8" on a €250 item) adds almost nothing to how the offer is perceived; our article on strikethrough pricing and its regulation covers the "rule of 100" (percentage under €100, amount above) — Weber-Fechner's Law is the precise psychophysical reason behind that empirical rule.
• A multi-tier pricing table — the gap between two plans also needs to be proportionally noticeable for a visitor to clearly tell their respective value apart; see our study of the compromise effect in a pricing table.
• Order bumps and upsells — an add-on offered at checkout is noticed less the smaller it is relative to the amount already committed; that's exactly what makes a well-sized order bump feel almost painless, while the same amount offered on its own, without anchoring, would feel like a real decision.
• Monthly vs. annual pricing — announcing a saving "of €96 a year" reads very differently from "€8 less per month" on the same service, even though the total amount saved is identical; our monthly vs. annual comparison covers this framing effect.
• A bundle vs. a single product — an €80 discount on a €229 bundle (roughly 35%) comfortably clears the noticeable threshold; the same €80 off a €900 item would stay below that threshold and barely register.

What a more recent study qualifies

Weber-Fechner's Law isn't a mathematical absolute that applies mechanically to every consumer. A more recent study by Ryan B. Larson and Alan Tauscher, "Examining price variation sensitivity with surveys and the relevance of Weber's law," published in 2024 in the Journal of Revenue and Pricing Management, surveyed US consumers about furniture purchases and shows the picture is more nuanced than the pure logarithmic model: a significant share of respondents notice and react to small price changes, well below the theoretical proportional threshold, and that sensitivity varies with a buyer's time preference, risk aversion, and social-desirability bias in self-reported answers. The practical takeaway for a landing page isn't to dismiss small discounts as scientifically invisible, but to treat the 15-20% threshold as a target to aim for rather than a strict floor below which a discount would be worthless.

The most expensive mistakes

• Showing an impressive absolute amount on an already-high price — "-€50" trumpeted on an €800 service is, proportionally, still a 6% discount: correct, but far from the "great deal" effect the bold number seems to promise.
• Stacking several small discounts — three 5% discounts stacked almost always register worse than a single discount announced at 15%, even when the final amount saved is identical.
• Comparing a monthly price to an annual price without reframing — presenting the saving in whichever unit shrinks its apparent size (per month rather than per year) effectively places the discount below the perception threshold yourself.
• Ignoring the threshold on an order bump — offering an add-on priced above 20-25% of the amount already committed pushes it out of the "painless extra" zone and turns it back into a full purchase decision, with all the hesitation that reintroduces.

How to apply this in practice this week

1. Calculate the actual percentage of every discount you display, not just its amount in currency, and aim for a 15-20% range to clear the perception threshold identified by Monroe.
2. Pick the unit that maximizes the perceived percentage: an annual amount rather than a monthly one, a per-user price rather than a per-team one, whichever makes the change most visible honestly.
3. Combine small discounts into a single, legible announcement rather than stacking them without clearly adding them up for the visitor.
4. Cap order bumps and upsells below a quarter of the amount already committed, so they stay perceived as a minor add-on rather than a fresh decision.
5. Test, don't assume: Larson and Tauscher's study is a reminder that price sensitivity varies by audience — an A/B test on a discount's amount or format remains more reliable than a general rule applied without checking.

LanderKit's own promotion mechanism applies this principle directly: the week's code brings a template down from €89 to €59, a discount of roughly 34% — comfortably above the noticeable threshold — and the full bundle drops from €229 to €149, a comparable proportional discount. The 10 LanderKit templates are built for launching a pricing grid, an order bump, or a promotion countdown that's already sized correctly; the single-product e-commerce template and the SaaS waitlist template each show a pricing structure where the gap between options stays proportionally legible. Our guide to the anchoring effect rounds this out for the part of the price that comes before the discount itself.