1099b what if you dont know cost or other basis in undetermined holding period

[KenH1 · Accepted solution]

For unreported cost basis:

Make a reasonable estimate, based on old trade confirmations or historical prices from a source such as www.finance.yahoo.com 

For unreported sales category:

If you held the security less than one year, use code C (short-term, not reported)

If you held the security more than one year, use code F (long-term, not reported)