How is float calculated?

Float is the shares outstanding minus any non-trading shares. The shares outstanding is not generally a subjective number, however, the “non-trading shares” is very subjective. Different providers have different methodologies for calculating this, but generally it includes (a) shares owned by strategic partners (ie, corporations, not financial institutions), and (b) shares held by insiders.

Shares reported in a 13F or 13G filing are generally considered trading shares so they do not affect float.

There is legitimate debate about whether or not shares held by index funds should be considered non-trading shares, since these funds must match the shares held in an index and are not likely to be sold as long as the company remains in an index.

We get Float from Capital IQ - one of the leading providers of financial data - and it is one of the most accurate you will find. They have a team of analysts that track filings and adjust this number on an ongoing basis.