Advertising claims: the proof you need before you publish

Substantiation is the part of advertising law that surprises people most: the burden sits with the advertiser before the claim runs, not after a complaint. You are not entitled to publish and then defend; you are expected to hold the evidence first.

Objective and subjective claims

The distinction decides almost everything. An objective claim can in principle be verified by someone else — a number, a duration, a comparison, a performance characteristic. A subjective claim expresses taste or judgment and cannot be settled by evidence.

Objective claims require substantiation. Subjective claims do not, but the exemption is narrower than it looks, because most claims that feel subjective have an objective core. “Lasts longer” is objective. “Feels more durable” is subjective until someone tests durability and the two words become interchangeable in the reader’s mind.

What counts as adequate substantiation

There is no universal bar, because the required level of proof scales with the claim. A modest claim needs modest support; an extraordinary claim needs evidence that matches it. Three questions usually settle whether what you hold is enough:

1. Is it competent? Produced by someone with the relevant expertise, using a method accepted in that field.
2. Is it reliable? Repeatable, with a sample and a method you could describe to a stranger.
3. Is it representative? About the product actually sold, in the circumstances the customer will meet, not an earlier version or a favourable case.

The claims that go wrong most often

• Comparatives. “Better than” requires evidence about the thing compared. If the comparison is against a named competitor you need evidence about their product, which you may not have.
• Numbers with no denominator. “Up to”, “as many as” and “saves up to” are the commonest evasions and the commonest source of complaints, because the qualifying word is small and the number is not.
• Testimonials used as proof. One customer’s experience is an anecdote. Presenting it as evidence of typical results turns an anecdote into a misleading claim.
• Claims about the future. “Will”, “guarantees” and “ensures” are promises, and the substantiation question becomes whether the promise can be kept for every buyer, not for most.

Wording so that the evidence you hold is sufficient

The cheapest fix is almost always narrowing. A claim scoped to what the test measured is defensible with the test you already ran; the same claim stated generally needs evidence you do not have.

Instead of “works in seconds”, say “in our test of [n] documents, the median time was [x]”. The second is longer, is true, and cannot be challenged — which is exactly what you want from a claim about performance.

The same move applies to conditions. A result obtained under stated conditions is a fact; the same result presented without conditions is an implication that it holds generally, and that is usually false.

Keeping the file

Keep the evidence, the wording, and the date together, and keep them for as long as the claim is live plus whatever retention period applies. Regulators can ask about a campaign that ended years ago, and a claim defended from memory is a claim you have effectively withdrawn.

The file should be readable by someone who was not there. If it consists of a slide with a number and no method, it is not a file; it is a reminder.

Who decides, by jurisdiction

The substantiation principle is close to universal among consumer protection regimes, but the enforcing body and the remedy are not. In the United States the Federal Trade Commission administers it and can require substantiation on request. In the European Union the Unfair Commercial Practices Directive sets the framework, enforced by national authorities. In the United Kingdom the Competition and Markets Authority enforces under the Digital Markets, Competition and Consumers Act 2024.

Where the product is health-related, a separate and stricter regime usually applies on top — see health and wellness claims. For how to test a claim before you write it, see marketing claims and evidence.

Where a claim travels further than the page

A claim is not confined to the advertisement. It appears in the listing that an affiliate writes, the comparison table a reviewer assembles, the summary a search engine generates, and the version of it a customer repeats to a friend. Each of those carries the claim without the qualification that sat beside it on your page.

The practical consequence is to write claims that survive being quoted. A sentence whose truth depends on a footnote, an asterisk or the paragraph above it is a sentence that will be misquoted, and the misquotation is still yours.

Claims made by others on your behalf

An agency, an affiliate, a reseller or a creator writing about your product makes claims in your commercial interest, and most regimes treat the advertiser as responsible for them. That means two obligations: brief them on what may be said, and check what was actually said.

The brief that works is short and specific: the claims that are cleared, the wording that has been approved, and the claims that may not be made under any circumstances. Vague guidance produces confident improvisation.