The baby shelf rule (General Instruction I.B.6 of Form S-3) caps annual shelf raises at one-third of public float value for issuers under $75M float. The intent is to protect shareholders of small companies from continuous dilution.
The execution creates the opposite incentive. Because the float calculation can use any closing price from the last 60 days, management is rewarded for pumping the stock before filing.
The exact formula
Public float value = float shares × any closing price within the last 60 calendar days. Companies always pick the highest closing price in that window — there's no SEC rule requiring the average or the most recent.
Maximum 12-month raise = ⅓ of that float value. Once total raises hit the cap, the shelf is frozen until either the rolling 12-month window resets prior raises or the float value gets recalculated higher.
Crossing the threshold
If new share issuance pushes the float value above $75M, the baby shelf restriction disappears entirely. The remaining shelf capacity is whatever's left under the original registered amount, minus prior 12-month raises.
This creates a cliff: a company that was capped at $9M can suddenly raise $40M+ the moment its float crosses $75M. Holders never see it coming because they're reading the 10-K disclosure that's already outdated.
The classic MBOT sequence
Microbot Medical, December 2019. Float = 3.93M shares.
Dec 20: highest 60-day close was $6.85. Float value = $26.9M, ⅓ cap = $8.97M, but the company had already raised $11.74M in prior 12 months. Result: cannot raise at all.
Stock pumped to $10.11. Float value = $39.7M. New capacity = roughly $1.5M. Still trivial.
Stock pumped to $16.28. Float value = $63.9M. New capacity = $9.59M. The company immediately filed an RDO on Dec 26 for $9,585,009 — exactly the maximum.
After that raise, new float = (3.93M + 0.91M new shares) × $16.28 = $78.8M. Above $75M — baby shelf no longer applies. New cap = $75M − prior raises = $43.5M of unused capacity. MBOT raised another $10M on Dec 27 and another $10M on Dec 30, with the stock dropping from ~$14 to ~$10 intraday on each print.
What to watch
Calculate the float value yourself before holding a sub-$75M-float name overnight. Float × highest close in the last 60 days. Subtract trailing 12-month raises from one-third of that number. If the remaining capacity is small, dilution risk is mechanical. If a price spike just expanded capacity into 8-figure territory, expect a raise within days.
The rule resets at the next 10-K filing — so the first available shelf use after a fiscal year boundary often comes faster than the prior year's pattern suggests.