How do I calculate RMD on a double inherited IRA? I inherited an IRA from my spouse who recently died. She inherited her IRA from her Mother years ago. Should I withdraw the RMD that she was planning to pay at year-end? How do I calculate future RMD?

Yes, take the RMD that she would have taken. You can roll her IRA into your IRA account. Your financial institution will calculate the required amount to withdraw. 

refer to IRS Pub 590B which covers this situation and any other situation you can think of.

Exactly where in IRS Pub 590B is this double-inherited-IRA question covered?  I have it in front of me and still can't find the answer.  Thanks.

@Robin53 

Please refer to "Death of a beneficiary" Page 9.

Perfect.  Thank you SO much.  Easy and exactly what I needed to know.  My appreciation!

IRS Pub 590-B has not yet been updated to conform to the recently proposed regulations regarding changes to the RMD requirements.  With regard to successor beneficiaries, the proposed regulations may or may not be made final in their present form.  A successor beneficiary might be subject to both annual RMDs and the 10-year rule or just the 10-year rule, but that won't be clear until the new regulations are finalized.