When do you have to file for percent ownership of a public company?

You must file for percent ownership of a public company when you acquire 5% or more of the company's outstanding shares. This requirement is mandated by the Securities and Exchange Commission (SEC) under Section 13(d) of the Securities Exchange Act of 1934. The filing must be done within 10 days of reaching the 5% threshold and involves submitting a Schedule 13D or Schedule 13G, depending on the purpose of the acquisition.