Greenshoe (Over-Allotment) Option
A clause in an IPO prospectus letting the underwriters sell up to about 15% more shares than the deal officially offers.
What it is
A greenshoe, formally an over-allotment option, is a clause in an IPO underwriting agreement that lets the underwriters buy additional shares from the issuer at the public offering price less the underwriting discounts and commissions, on top of the shares in the base offering. The conventional size is up to 15% of the base offering — a ceiling backstopped by FINRA Rule 5110, which subjects an over-allotment option above 15% of the amount offered to the underwriting-compensation restrictions — exercisable for a limited window after pricing (conventionally 30 days from the date of the prospectus). The name comes from the Green Shoe Manufacturing Company, which first used the structure in a 1963 secondary offering of its common stock. Mechanically it exists so underwriters can over-sell the deal and then cover that short position either by exercising the option or by buying shares in the aftermarket. That aftermarket buying is a syndicate covering transaction — one of the activities Rule 104 of Regulation M permits in connection with an offering, alongside stabilising bids and penalty bids. The greenshoe is the contractual term that supplies the short position, not the legal authority for stabilisation. The exact share count and exercise terms are stated in the final prospectus — the 424B4 for a US listing.
Why it matters
The greenshoe changes the arithmetic of an IPO: the shares actually sold, the proceeds raised, and the resulting free float can all be up to 15% larger than the headline offering, so comparing deals on the base number alone understates the ones where the option was exercised. It also sits at the centre of post-IPO price support — Rule 104 of Regulation M is what permits stabilising bids, syndicate covering transactions and penalty bids, and the greenshoe is what gives underwriters the covered short position they work from — which is why early aftermarket trading in a new listing is not a clean read of unassisted supply and demand. Because the count sits in the prospectus, it is a hard filing fact rather than an estimate, which makes it a consistent basis for comparing potential float and dilution across a cohort of listings. A pitfall is reading the greenshoe as a demand indicator: its presence is boilerplate on nearly every underwritten IPO and says nothing about interest in the deal, while its exercise or non-exercise is disclosed only after the fact and reflects underwriter short-covering economics, not a verdict on the company. The size disclosed in the prospectus is a ceiling on what may be exercised, not a statement of what was — so the parsed count gives the maximum potential float, never the realised one.
How it's calculated
There is no model or estimation here — the greenshoe is a contractual term read directly from the filing. The 424B4 final prospectus states the base number of shares offered and, separately, the additional number of shares the underwriters may purchase under the over-allotment option, at the public offering price less underwriting discounts and commissions, along with the exercise window (conventionally 30 days from the date of the prospectus). The implied percentage is simply greenshoe shares divided by base offering shares, which conventionally tops out at 15% — a ceiling backstopped by FINRA Rule 5110 rather than by custom alone. Maximum total shares is the base plus the full greenshoe; whether the option was actually exercised is disclosed only after the fact, so this is a ceiling rather than a realised figure. Quintarthai's IPO screener parses the greenshoe share count out of the 424B4 text and stores it as a filing fact, so no assumption or coefficient is involved.
How Quintarthai uses it
Quintarthai's IPO screener parses the greenshoe (over-allotment) share count directly out of the 424B4 prospectus and shows it alongside the other parsed filing facts — the lock-up period with a verbatim quote, Form D private-placement history, and PCAOB Form AP auditor data. It is presented as a disclosed filing fact for research context, never as a signal about demand or an indication to act; see /app/.