What Makes Information Material and Non-Public

"Material non-public information," or MNPI, sounds like it should be a checklist — a fixed set of facts (earnings before release, an unannounced merger, a drug trial result) that are automatically off-limits to trade on. It isn't a checklist. Both halves of the phrase, "material" and "non-public," are legal tests applied to specific facts and specific circumstances, and the same piece of information can be material in one context and immaterial in another.

Two separate questions, both must be yes

Question	The test	Common failure to appreciate
Is it material?	Would a reasonable investor consider it important to a decision to buy, sell or hold?	Materiality is about probability and magnitude combined, not certainty — a low-probability but huge-impact event (an early-stage merger talk) can still be material
Is it non-public?	Has it been disseminated broadly enough, and had enough time to be absorbed, that the market has genuinely had a fair chance to react?	A fact mentioned once in an obscure filing is technically "public" but courts and regulators look at whether dissemination was genuinely adequate, not just technically compliant

Information only counts as MNPI when both boxes are checked simultaneously. A fact can be extremely material and still perfectly tradeable if it's genuinely public — that's just called research. A fact can be completely non-public and still not create liability if it's immaterial — knowing a company's office carpet is being replaced next week is non-public and irrelevant.

Why "probability times magnitude" matters

Early-stage merger negotiations are the textbook hard case. At the very first exploratory conversation between two companies, there's a real chance nothing ever happens — most preliminary talks don't become deals. Courts have held that even at that early stage, the information can still be material, because the magnitude of a completed merger (typically a large, sudden price move) is large enough to offset the low probability of it actually closing. Materiality doesn't require near-certainty; it requires that a reasonable investor would want to factor the possibility in, weighted by how big the outcome would be.

When does public information actually become "public"

Regulation FD in the US requires public companies to disclose material information broadly — via a press release or public filing, not selectively to favored analysts or investors — and specifies that information isn't properly public until it's had a real chance to be absorbed by the market, not merely released into it. Trading in the narrow window between an announcement and the market actually digesting it is still treated cautiously by compliance functions, even though the information is technically no longer secret. The disclosure-side rules that create this timing are covered in Regulation FD and Selective Disclosure.