There was actually
a current thread about this on Boggleheads:
Bogleheads • View topic - How long will my inherited ira last?
And as happens at times, I learned a HUGELY valuable piece of advice that avoided a huge error I (and a few other posters) were making on inherited IRAs.
If the IRA beneficiary is a non-spouse, you only use the age the first year of distributions, then modify the divisor after that:
If the decedent passes away in 2012, and did not already take their RMD in 2012 before they passed on, then their estate takes out the RMD and places the money in the estate. 2012 is complete (as far as RMDs go).
In 2013, the beneficiary has to take out their first RMD. They use their age on December 31, 2013 in the Table I, to determine the divisor, and then take out their RMD.
However, for years 2014 and later, you don't go back to Table I - you need to subtract 1 from the divisor to determine your RMD.
Example: if you're age 50 on December 31, 2013, then your divisor on 2013 is 34.2.
But for 2014, you subtract 1, so your divisor is 33.2 (not the age 51 divisor of 33.3).
And for 2015, you subtract another 1, so your divisor is 32.2.
Continued on down, one poster on Boggleheads noted that at one point, reducing the divisor by 1 each year will eventually create an RMD divisor of less than 1 (in this example, at age 84, the divisor will be 0.2, which means you will, in theory, have to withdraw a minimum of 5 times the value from the prior year.
).