HOW DO YOU KNOW HOW MUCH OF THE DOLLAR AMOUNT APPLIES TO TO THE RMD THAT NEEDS TO BE TAKEN OUT

[fanfare]

you, or your custodian for you, will calculate the RMD. Then take out at least that much.

[JotikaT2]

The Required Minimum Distribution (RMD) is actually a fixed amount that must be taken out each year once you reach 70 1/2 each year.  Your plan administrator should be following the rules to ensure you are taking the RMD. 

Attached is a link to the IRS worksheet if you need to determine what amount is.

RMD Worksheets - IRS

Also is a link with more information on RMD's.

What is a RMD help article