The baby shelf rule: how General Instruction I.B.6 caps small-company shelf sales
Below $75 million of public float, a listed company can still use Form S-3, but only up to one-third of float per 12 months. Learn the math from a real filing and the 2026 changes.
The rule in plain English
Form S-3 is the short-form registration statement that makes shelf offerings practical. For primary offerings, the main route is General Instruction I.B.1, which requires at least $75 million of public float.
A company below that line can still use Form S-3 under General Instruction I.B.6, which traders call the baby shelf rule, if:
- it is not a shell company (and has not been one for at least 12 months),
- it has a class of common equity listed on a national securities exchange, and
- the securities it sells under I.B.6 in any 12 calendar months, including the sale, total no more than one-third of its public float.
The rule does not cap the shelf's registered amount. A company may register $100 million on a baby shelf. It caps how much can be sold under the instruction in a rolling year.
The formula
Public float = non-affiliate shares × price
I.B.6 capacity now = (1/3 × public float) − I.B.6 sales in the prior 12 calendar months
The instruction's own notes fill in the details:
- Price: the last sale price, or the average of bid and ask, in the principal market on a date within 60 days before the sale. The company picks the date within that window, which is why the price in a filing may be well above the current quote.
- Affiliates: the Rule 405 definition. Shares held by officers, directors and controlling holders are typically excluded.
- Warrants and convertibles sold under I.B.6 count at the market value of the maximum underlying shares, not at the price paid for the derivative.
- Upgrade: if public float later reaches $75 million or more, the one-third limit stops applying to later sales under that registration statement.
Two staff interpretations that explain most of the paperwork
SEC staff interpretations add two mechanics that show up again and again:
- Measured on the offered amount. Remaining capacity is measured just before each takedown and applies to the amount offered in that prospectus supplement, not the amount later sold (Interpretation 116.22). For an ATM, the supplement cannot offer more than current capacity even if sales will be slow.
- Concurrent programs add up. If an earlier continuous offering, like an ATM, is still open, its unsold amount also counts against capacity for a new takedown (Interpretation 116.23).
So when a baby-shelf company's float rises or its rolling 12-month window frees up, it often files a new supplement to raise the ATM ceiling to the new capacity. Those small "up to $X" supplements are the baby shelf rule at work.
Walkthrough: Sonoma Pharmaceuticals, June 18, 2026
Source: Sonoma Pharmaceuticals, Inc. 424B5 supplement dated and filed June 18, 2026 (Registration No. 333-275311). It supplements an ATM prospectus supplement dated September 26, 2025, which itself supplements a base prospectus dated November 20, 2023. Figures are quoted or derived from that filing.
Step 1: the starting ATM
The September 26, 2025 supplement registered ATM sales of up to $2,070,463. From then through June 18, 2026, the company sold 173,073 shares for $574,633, leaving $1,495,830 unsold under that ceiling.
Step 2: public float, as the filing computes it
- Shares outstanding: 4,785,801, of which 4,773,212 held by non-affiliates.
- Price: $2.65, the closing price on April 20, 2026.
- Public float: $12,649,011.
Check: 4,773,212 × $2.65 ≈ $12,649,012. Also check the date: April 20 to June 18, 2026 is 59 days, inside the 60-day window. The filing does not say why that date was chosen; it only states the price and date.
Step 3: the capacity arithmetic
1/3 × $12,649,011 ≈ $4,216,337
$4,216,337 − $574,633 (I.B.6 sales in prior 12 months) ≈ $3,641,704
The filing states $3,641,703 available; the $1 difference is rounding.
Step 4: what the supplement actually does
It raises the ATM's maximum aggregate offering price from $2,070,463 to $3,641,703, a figure that includes the $1,495,830 still unsold. Our arithmetic: the new room above the old remainder is $3,641,703 − $1,495,830 = $2,145,873.
Step 5: put it in shares, carefully
At the $2.65 price used for float, $3,641,703 would be about 1.37 million shares, roughly 29% of the 4,785,801 outstanding. That is an upper-bound illustration at one price. ATM sales happen at market prices, and as of June 18, 2026 none of the new capacity had been used. Actual sales must come from later 10-Q reports or supplements.
A second cover to compare
Dyadic's August 13, 2026 registered direct 424B5 (Lesson 11) states public float of $45.4 million from 30,888,304 non-affiliate shares at $1.47, the July 21, 2026 close, which that company describes as the highest close within 60 days. It reports no I.B.6 sales in the prior 12 months and capacity of up to $15.1 million. Two companies, two different price-date explanations; quote each filing's own wording.
How the rule can be stretched, and what staff said
Interpretation 116.25 addresses a company that sells part of a deal off a baby shelf and the rest in a private placement registered for resale on another Form S-3. Staff view that structure as evading the limit: the resale securities count against I.B.6 capacity. When you see a shelf takedown paired with a large private placement to the same investors, check how the filing treats capacity. Do not assume a motive the filing does not state.
What changed in 2026
March 19, 2026: a new staff interpretation (116.26). If a company sets up an ATM while eligible under I.B.1 ($75 million or more of float), files the ATM supplement, and later drops below $75 million at its next annual update (the Section 10(a)(3) update), staff will not object if it keeps selling the full amount of that previously filed ATM supplement, even above the I.B.6 limit. The interpretation is dated March 19, 2026 on the SEC's Securities Act Forms page. The SEC now labels this guidance "Corporation Finance Interpretations" (CFIs); older links to "Compliance and Disclosure Interpretations" (C&DIs) redirect to the new pages, as checked on October 5, 2026.
May 19, 2026: a proposal to eliminate the baby shelf. In Release No. 33-11418, "Registered Offering Reform", the Commission proposed to remove Form S-3's transaction requirements, including the $75 million float test and General Instruction I.B.6, so that issuers meeting the proposed registrant requirements could use Form S-3 without the one-third cap. The proposal was published in the Federal Register on May 26, 2026, and comments were due July 27, 2026.
Status as of October 5, 2026: proposed, not adopted. The SEC's rulemaking page for File No. S7-2026-17 still lists it as a proposed rule. Until a final rule is adopted and effective, I.B.6 applies as written. Verify status again before relying on this paragraph.
Reading the next baby-shelf cover
- Public float, the non-affiliate share count and its date, and the price and its date.
- I.B.6 sales in the prior 12 calendar months.
- Stated remaining capacity; recompute it.
- Whether another continuous offering is still open and counting against capacity.
- Whether the supplement re-sizes an existing ATM, and the new ceiling versus unsold remainder.
Remember one line
Baby-shelf capacity is one-third of a dated public float minus a year of sales; it is a ceiling that moves with price, not a plan.