I received a 1099B which shows covered shares (both short and long term) with the cost basis. However, I have some non covered shares with no cost basis. Can you tell me how to figure out the cost basis for these non covered shares? Or where to find the information on how to calculate cost basis for non covered shares?
The following link will provide you with information on how to determine the cost basis for non covered shares
What is the actual formula to calculate it from the historical statements? accounting for capital gain and dividend reinvestments?
There isn't a "formula" per se. You will have to treat each reinvestment of dividends and capital gains as a separate purchase for the purpose of cost basis determination.
Often, it can be helpful to gather all of the transaction confirmations of the transactions and build a spreadsheet to help you and then program the spreadsheet to calculate the average cost.
If you use a full-service broker the broker will often do this for you as they have the information most of the time, they just don't print it on the 1099-B.
Your broker should be able to provide you with the confirmations or historical statements that will have this information or, if you have online account access the statements/confirmations should be there.