About 20 years ago my Grandmother bought a mutual fund with her and I as joint tenants.?

She passed on about 3 years ago. How would I go about establishing a cost basis for the shares if I were to sell this Fund?

I believe, if you are a joint tenant, that your cost basis is when the shares were originally purchased. By the way, you should contact the fund to have her name removed if you haven't already. You now own these shares as sole owner.

Check with a tax accountant, not a lawyer. Lawyers don't normally deal with this kind of issue.

only a lawery will really be able to tell you more.

The financial institution that she purchased the mutual fund with should be able to provide this information. If not, you could determing a cost basis by taking the current account value and reverse calculating the purchase price based on dividends. The federal government really wants a good faith estimate of what the cost basis is.

Call the company that holds the mutual fund. Some of them house cost basis information, and some of them don't. You might get lucky and they will calculate it for you and send it to you. Otherwise, they will send you all the information you will need to calculate it. I would suggest seeing a tax advisor to have them calculate it for you if the latter is the case.

Also, be sure to ask them what documentation you will need to redeem. In most cases it would be a certified copy of the death certificate and a signature guaranteed letter with your signature stating that your grandmother has passed and you would like to redeem the account in full.

Check this book out. It's a guide for people asking questions about basic investing principles and how-to's. I'm sure you can find something here in mutual funds.

Forget the lawyer.

Probably the easiest way to do this is to ask the fund to give you a statement showing your purchases since day one. They get these kinds of requests all the time. (Or, if the fund was sold to you by a brokerage or investment firm, start there).

The more interesting question might be whether you calculate your gain (or loss) based on the average cost of all shares, or on the cost and sale prices of specific lots of shares. You are allowed to match things up so that you have the least gain. But your CPA may need to do this for you if the scenario is a complex one. Timing may be everything -find "losers" to sell in a high tax year, sell the big gainers in a low tax year. Thus, you may NOT want to cash in all the chips at once.