You can look at individual IPOs. The most high profile one recently was Airbnb. According to the NYT [0], they sold $3.5 billion worth of shares, at a valuation

You can look at individual IPOs. The most high profile one recently was Airbnb. According to the NYT [0], they sold $3.5 billion worth of shares, at a valuation of $47b, so only 6%. For another example, Mark Zuckerberg still owns 30% of Facebook, 8 years on from the IPO. You're correct that the whole company "goes public" at the same time. But that just means it becomes legal to sell shares to small investors, and the company becomes subject to the reporting requirements, etc. The previous owners still typically own most of the shares, and (almost always) are forbidden to sell them for around 6 months after the IPO. [0] https://www.nytimes.com/2020/12/09/business/airbnb-ipo-price.html https://www.nytimes.com/2020/12/09/business/airbnb-ipo-price...