Why an IPO sells more shares than planned
IPO filings often show two figures, such as 10 million base shares and an over-allotment option of 1.5 million. Underwriters allocate more shares to investors than planned and settle the difference later. The right that lets them settle the extra shares is commonly called a greenshoe option.
This guide explains the sequence of over-allotment and the greenshoe, then compares with hypothetical scenarios how underwriters close their position when the stock trades above or below the offer price after listing. It shows how the issuer's proceeds change and what to check in the filings.
How over-allotment works
Investor.gov describes an IPO as a company's first sale of shares to the public. When demand is strong, underwriters allocate more shares than the base deal, for example 15% more. The extra shares are usually delivered first from shares borrowed from existing holders, so the underwriters end up owing shares, a position similar to a short sale.
Underwriters close that position in one of two ways: by exercising the greenshoe option to buy additional shares from the issuer at the offer price, or by buying shares in the market after listing. Which they choose depends on whether the stock trades above or below the offer price.
Hypothetical scenarios
The table assumes an IPO priced at $20 with 10 million base shares and a 1.5 million share (15%) over-allotment. It compares how the underwriters close the position and how much the issuer raises, depending on the post-listing price. Underwriting fees are left out.
| Post-listing price | Covered by market purchases | Greenshoe exercised | Final shares issued | Issuer's gross proceeds |
|---|---|---|---|---|
| Rises to $25 | 0 | 1.5 million | 11.5 million | $230 million |
| Around $20 | 0.5 million | 1.0 million | 11.0 million | $220 million |
| Falls to $18 | 1.5 million | 0 | 10.0 million | $200 million |
When the price rises, exercising the option at $20 is cheaper for underwriters than buying at $25. When it falls, buying at $18 in the market is cheaper, and that buying supports the price.
What stabilization means
When the stock falls below the offer price, underwriters buying in the market create demand that can slow the decline. U.S. rule 17 CFR 242.104 sets conditions for stabilizing transactions in connection with an offering and for syndicate covering purchases that close the underwriters' short position.
This is not a promise to hold the price at any level or protect investors from losses. Underwriters can buy only up to the size of the over-allotment, and once that buying ends, so does the support. After the 1.5 million shares in the third row are bought, the price is set by other investors' supply and demand.
Effects on the issuer and existing holders
When the greenshoe is exercised, the issuer sells additional shares and receives more money. In the table, rising prices lift proceeds from $200 million to $230 million and shares issued to 11.5 million, diluting existing holders accordingly.
Sometimes the option attaches to shares sold by existing shareholders rather than new shares. Then the extra proceeds go to the selling holders, not the company. Check whether over-allotment shares are primary or secondary to know how much money the company actually receives.
The distinction also affects how to read headlines. A report that an IPO raised a certain amount including the over-allotment may combine money paid to the company with money paid to selling shareholders, two very different things for the company's balance sheet.
Reading the filings
For U.S. IPOs, check the registration statement and final prospectus on SEC EDGAR; for Korean IPOs, the registration statement on DART.
- Find the number of base shares and over-allotment shares, and the ratio between them.
- Check whether over-allotment shares are newly issued or sold by existing holders.
- Note the greenshoe's exercise period and price, usually the offer price less the underwriting discount.
- After listing, look for disclosures of how much of the option was exercised and whether any position was covered in the market.
- Review lock-up periods and release dates to see when supply might increase.
What the exercise outcome tells you
A disclosure that the greenshoe was fully exercised can signal that the stock mostly traded above the offer price after listing; no exercise suggests the underwriters covered in the market. Both describe a past period and say nothing about where the price goes next.
When the exercise period ends, stabilizing purchases end too. If lock-up expirations fall around the same time, supply may increase, so it helps to put the disclosed dates on a single calendar.
Limits of the analysis
The prices and share counts here are hypothetical. Actual over-allotment ratios, exercise periods, and stabilization rules vary by country and deal, and Korean IPOs operate over-allotment differently in detail from U.S. deals.
When looking at a real offering, check the latest registration statement and prospectus with their dates. This guide does not recommend subscribing to any offering or trading any security.