The APA sets a 30-day floor before final rules take effect, absent an exception. Among 2,060 rules published in 2026 so far, 209 land on exactly that floor — while 29 days appears just 5 times.

The Federal Register published 2,060 final rules between January 1 and September 7, 2026. Of those, 1,859 carried a specific effective date in the agency filing. The most common gap between publication date and the date a rule takes effect was zero: 568 rules (30.6% of those with effective dates) published and became effective the same day. The Administrative Procedure Act permits this for certain categories — rules granting exemptions, interpretive rules, and rules supported by a published "good cause" finding. Among rules that gave any advance notice, the most common non-zero notice period was exactly 30 days: 209 rules, or 11.2% of the 1,859 with effective dates — the peak of the distribution, ahead of 35 days (165), 32 days (121), 31 days (73), and 15- and 60-day gaps (43 each), with no other gap higher. Exactly 29 days appeared 5 times. The ratio at the statutory boundary was 42 to 1 [verified, Federal Register API, all RULE-type documents January 1–September 7, 2026, publication_date and effective_on fields, retrieved September 8, 2026]. Section 553(d) of the Administrative Procedure Act sets the floor: a final rule 'shall be made not less than 30 days before its effective date.' It names 30 days as a minimum, not a target. In the data, 30 days is also the most common non-zero gap. The pattern precedes 2026. Full-year 2024 shows 396 rules at exactly 30 days against 5 at 29 — a 79-to-1 ratio. Full-year 2025 shows 169 against 9 — 19 to 1. Across all three years combined, 29-day rules have appeared 19 times; 30-day rules, 774 times [verified, same API, 2024 full year n=2,900 with effective dates; 2025 full year n=2,187; 2026 through September 7 n=1,859]. A secondary concentration appears at exactly 35 days: 165 rules in 2026. Of those, 163 came from the Transportation Department — nearly all FAA airworthiness directives. A 35-day gap is five calendar weeks; the concentration is consistent with ^sspeculative a fixed FAA scheduling cycle for that instrument type. The 35-day cluster draws from a different set of rules than the 30-day one. The 30-day rules, by contrast, spread across agencies: Transportation (48), Interior (23), Environmental Protection Agency (20), Homeland Security (16), Agriculture (12), Federal Communications Commission (10), Treasury (10), Justice (9), and others [verified, same pull]. Agencies are attributed by the Federal Register's primary-agency field; a rule listing a parent department and a sub-agency is counted once, under the parent.

The following is analysis, not fact. The APA's 30-day floor does not instruct agencies to pick 30 days. It tells them they may not pick fewer than 30 days (absent an exception). Choosing 30 days requires no exception and no published finding; setting a shorter window generally does. The 30-day floor is strongly associated with where agencies cluster ^mmodeled. That association is consistent with agencies treating the minimum as the obvious default rather than a floor to calibrate rule by rule ^mmodeled, but the distribution shows a correlation, not a mechanism that determines the choice. The 42-to-1 ratio at the statutory boundary is a pattern, not a mandate. What sits on the 29-day side of the line are five rules: that number is small enough that individual circumstances — a specific deadline, a correction, an exception the agency filed — could explain all of them. What sits at 30 days is 209 rules, spanning at least eight agencies and a wide range of regulatory categories. The concentration at 30, and the near-absence at 29, appear consistent with the statutory line rather than with chance ^mmodeled — a correlation the distribution shows, not a demonstrated cause. The FAA's 35-day cluster shows that agencies can and do depart from 30 days. A 35-day gap is five calendar weeks; the cluster is consistent with ^sspeculative a fixed scheduling cycle for airworthiness directives, which would give operators a predictable compliance window. That 163 of 165 thirty-five-day rules in 2026 came from a single agency — most of them FAA airworthiness directives — shows the spike is agency-specific, not a general tendency toward longer notice. The three-year consistency of the low 29-day count is harder to dismiss as coincidence ^mmodeled. Whatever might account for it — legal friction, drafting convention, or institutional default ^sspeculative — the same low count holds in each of the three years, under two administrations, across thousands of rules. That consistency appears more consistent with a feature of how the statute is read in practice than with a policy choice any particular administration made ^mmodeled — an association that holds across the years, not a proven cause.

The view that 30 days is too short has academic backing. The APA was enacted in 1946; the volume and complexity of modern federal rulemaking were not its drafters' frame of reference. Critics argue that 30 days is insufficient for industries, small businesses, or affected communities to adjust operations, seek legal advice, or negotiate compliance approaches — and that agencies setting the minimum by default, rather than by a judgment about what each rule requires, produces systematic underprovision of notice. Some proposals in Congress have sought to extend the floor to 60 days for rules above a certain economic threshold. The view that 30 days is appropriate points out that affected parties typically had 60 or more days to comment on the proposed rule before the final version was ever issued; that the final-rule effective date notice is a different mechanism for a different purpose; and that requiring longer windows by default would slow the regulatory process for time-sensitive rules — emergency safety standards, seasonal fisheries adjustments, aviation directives — without adding meaningful opportunity for compliance preparation in most cases. The data does not settle which view is correct. It shows that 30 days is where agencies cluster, consistently, and that the cluster sits on the statutory minimum ^mmodeled — an association the distribution documents, not a mechanism it proves.

Reading the distribution without the statutory context, the spike at 30 days looks like a bureaucratic convention — agencies picking a round number. Add the statute and the round number lines up with the APA floor ^mmodeled. The near-zero count at 29 days is the sharper finding. It is not that rules at 29 days are somehow impractical; a plausible reason is that going below 30 days generally invites a legal justification that 30 days does not ^mmodeled. The concentration in the data sits at a round number that is also a statutory threshold — and it shows up in each year: the Biden final year (2024), the Trump transition year (2025), and the Trump second year (2026 through September). The APA's minimum, set in 1946, is strongly associated with where the regulatory calendar lands ^mmodeled — the distribution shows the alignment, not that the statute determines it.