Ten year plus differences require use of different information to calculate Required Minimum Distributions from your IRA
If your spouse is ten or more years younger than you are, calculating the Required Minimum Distributions from your IRA is different than if you were closer in age.
Kiplinger's article "Retirement Distributions When Your Spouse Is Much Younger," explains that most people use Life-Expectancy Table III, the Uniform Lifetime Table, in Appendix B of IRS Publication 590 to calculate their required minimum distributions ("RMD"). However, if your sole beneficiary is a spouse who is more than 10 years younger than you, then you should use Life-Expectancy Table II, the Joint Life and Last Survivor Expectancy, to determine your RMD. That table requires you to withdraw less money each year than you would if your spouse were older.
Here's an illustration: if you're 70½ in 2015 and need to take your first RMD, you would divide your account balance as of the end of 2014 by 27.4. So if you had $100,000 in your account, you'd need to withdraw $3,649.64. But if your sole beneficiary is your wife, age 53, you'd divide your account balance by 32.6 and would need to withdraw only $3,067.48.
In Life-Expectancy Table II, look for your age on the left side of the table, then find where that line intersects your spouse's age on the top. Some RMD calculators will let you input your spouse's birthdate to determine your RMD, even if you need to use the different life-expectancy table.
You should also make sure your IRA administrator knows your spouse's birthdate, so they will use the correct table when calculating your RMDs—particularly if you have automatic RMD withdrawals.
At the same time that you are taking care of these tasks, check your beneficiary designations to make sure that they reflect your current life. The beneficiary designations on your retirement accounts and life insurance policies will guide their distribution, regardless of what your will says. Even if you have updated your will, you could still give your ex-spouse your IRA or the proceeds from your insurance policies. This happens more often than you'd think!
Reference: Kiplinger (December 16, 2015) "Retirement Distributions When Your Spouse Is Much Younger"