What is this total cost basis on an inheirted IRA?

[hrslady59]

and how do I calculate it

[RichardG]

Unless the deceased account owner made nondeductible contributions to the IRA (that's not likely), you have no basis in the account.  Inherited IRAs are known as "income in respect of a decedent," which mean you continue to pay income tax on distributions from the account just like the former account owner did.  The most likely answer is zero.