Generally, the required minimum distribution (RMD) must be figured separately for each account. You can calculate the RMD for each account that is not an inherited account by dividing the prior December 31 balance of a traditional (Non-Roth) IRA or retirement plan account by a life expectancy factor that the IRS publishes in tables in Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs). Use the:

• Uniform Lifetime Table (Table III) if you're an unmarried owner, an owner whose spouse isn't the sole beneficiary of your account, or an owner whose spouse isn't more than 10 years younger; or
• Joint Life and Last Survivor Table (Table II) if you're a married owner whose spouse is both more than 10 years younger and the sole beneficiary of the account. 

You can use "Worksheet 1-1. Figuring the Taxable Part of Your IRA Distribution" in Publication 590-B.

Note: Generally, if you have more than one traditional (Non-Roth) IRA, you can total the required distributions for all such IRA accounts for which you are the original owner and then satisfy the requirement by taking distributions from any one (or more) of the traditional (Non-Roth) IRA accounts. You cannot total the required distributions for a traditional (Non-Roth) IRA with a Roth IRA account. Nor can you total the required distributions for a traditional (Non-Roth) IRA for which you are the original owner with a traditional IRA that you hold as the beneficiary of a decedent (Inherited IRA). 

Lifetime RMDs are not required to be made from a Roth IRA for which you are the original owner. RMDs from such a Roth IRA begin after your death.

Distributions from an Inherited IRA are generally determined using the Single Life Expectancy Table (Table I) in Publication 590-B. However, the rules are complex and depend on several factors that are described in Publication 590-B.  

For more information, refer to Retirement plan and IRA required minimum distributions FAQs, Publication 590-B for RMDs from IRAs and Publication 575, Pension and Annuity Income for RMDs from employer-sponsored retirement plans, such as 401(k) plans.