Quick Answer
The greenshoe (over-allotment option) lets underwriters purchase up to 15% of the base offering in additional shares from the issuer at the offering price (less the gross spread) for a period of typically 30 days from the offering date. Underwriters use the greenshoe to over-allocate the deal short and cover the short either by exercising the option (issuer issues new shares, used when the stock trades above the offering price) or by buying shares in the open market (used when the stock trades below). The greenshoe is the only SEC-sanctioned post-pricing stabilization mechanism in the US.
The greenshoe is the deal's safety net. It is disclosed in the prospectus, baked into the underwriting agreement, and exercised (or not) based on how the stock trades in the days after the offering.
Structure of the Greenshoe
The greenshoe is a contractual option granted by the issuer to the underwriting syndicate.
- Maximum size: Underwriters may purchase up to 15% of the base offering in additional shares from the issuer at the offering price (less the gross spread)
- Exercise window: Typically 30 days from the offering date
- Pricing: Same offering price as the original deal, minus the same gross spread
- Purpose: Lets underwriters over-allocate the deal short and cover the short either by exercising the greenshoe (issuer issues new shares) or by buying shares in the open market (stabilization)
Worked example. A 10 million share base IPO at $20 with a 15% greenshoe.
- Maximum greenshoe = 1.5 million shares
- Maximum total offering = 11.5 million shares (base + greenshoe)
- Underwriters typically over-allocate by allocating 11.5 million shares to investors, creating a 1.5 million share syndicate short
- The short is covered by either exercising the greenshoe (issuer issues 1.5 million new shares) or buying 1.5 million shares in the open market
Exam Tip: Gotchas
- The 15% cap is on the BASE offering size, NOT the total offering. A 10 million share base IPO permits a greenshoe of up to 1.5 million shares. Total maximum offering = 11.5 million shares.
- The exercise window is 30 days from the offering date. Underwriters that fail to exercise within 30 days lose the option.
- The greenshoe is the ONLY SEC-sanctioned post-pricing stabilization mechanism in the US. Combined with stabilizing bids, it is the entire toolkit for legal price support; anything else is potential manipulation.
Exercise Decision Tree
The decision whether to exercise the greenshoe is driven by where the stock trades in the aftermarket.
| Aftermarket Behavior | Greenshoe Action | Why |
|---|---|---|
| Stock trades above offering price | Exercise greenshoe | Open-market cover would push price higher and cost more; issuer-issued shares cover the short cheaply at the offering price |
| Stock trades below offering price | Cover via open-market purchase (stabilizing bid) | Buying in the market supports the price AND covers the short at a discount to the offering price |
| Mixed: stock around offering price | Partial exercise + partial open-market | Optimizes between issuer proceeds and aftermarket support |
When stock trades above offering price. The underwriters exercise the greenshoe. The issuer issues the additional shares at the offering price, the underwriters deliver them to the over-allocated investors, and the issuer collects additional net proceeds. The aftermarket price stays where it is (no buying pressure from the syndicate).
When stock trades below offering price. The underwriters buy in the open market to cover the syndicate short. The buying pressure supports the price (legal stabilization), and the underwriters cover the short at a price below the offering price, capturing the spread between the offering price and the cover price as a hedge against placement risk. The issuer does not issue additional shares.
Think of it this way: the greenshoe is structured to give underwriters a free option that protects them in either direction. If the stock pops, exercise the option, deliver issuer shares, and pocket the extra commission. If the stock sags, buy in the open market, defend the offering price, and cover the short at a discount. Either path leaves the syndicate flat on shares with revenue earned.
Exam Tip: Gotchas
- Stock above offering price = exercise the greenshoe (issuer issues shares). Stock below = open-market cover (stabilizing bid). The decision is driven by which path minimizes the syndicate's cover cost.
- A partial exercise is common. A mixed aftermarket (stock briefly above, then sagging) often produces partial greenshoe exercise plus partial open-market cover.
Greenshoe in the Prospectus
The greenshoe is disclosed in the prospectus as part of the offering structure.
- The disclosure states the maximum size (up to 15% of the base)
- The disclosure states the exercise window (typically 30 days)
- The disclosure identifies the underwriters as the parties that hold the option
- The disclosure notes that the underwriters may engage in stabilizing transactions and that those transactions may be discontinued at any time
The prospectus does not commit the underwriters to exercising or to stabilizing; it discloses the possibility.
Exam Tip: Gotchas
- The prospectus discloses the greenshoe but does not commit the underwriters to exercising it. Whether to exercise is the underwriters' decision based on aftermarket trading.
- Stabilizing transactions are also disclosed as a possibility, not a commitment. The underwriters may stabilize; they are not required to.