You probably haven't marked your half birthday since preschool, but Uncle Sam is gleefully rubbing his hands together as the leading edge of baby boomers starts turning 701/2in July.

Why? The IRS doesn't want everyone delaying paying taxes on their retirement savings forever. At 701/2, you must get serious about your strategy for taking required minimum distributions from your tax-deferred retirement savings and paying taxes on the proceeds.

Learn the rules for your first RMD

You are required to start taking RMDs from your traditional IRAs (but not Roth IRAs) and other retirement accounts after you reach age 701/2. If you were born between January 1 and June 30, 1946, you must decide whether to take your first RMD this year or take advantage of a one-time-only option to delay your first withdrawal until April 1 of next year. From then on, you must take withdrawals by December 31 every year, including taking your second withdrawal at age 71 by the end of 2017. If you were born between July 1 and December 31, 1946, you can wait until next year to take your first RMD (or postpone it into 2018).

Note that taking two RMDs in one year could boost some of your income into a higher tax bracket. That could affect the amount of your Social Security benefits that is taxable or trigger higher Medicare premiums.

Calculate your RMDs

Your minimum payout is based on the balance in each account at the end of the previous year and a life-expectancy factor determined by the IRS. You must calculate the amount separately for each traditional IRA, as well as for any Simplified Employee Pension accounts (SEP-IRAs) and Simple IRAs. For 2016, use the account balance on December 31, 2015, then divide it by the life-expectancy number for age 70 in IRS Publication 590-B.

Add up the required minimums for each of your IRAs. You can take all of the money from one or more of your traditional IRAs, SEPs or Simple IRAs. If you don't take the required withdrawal by the deadline, you face a penalty of 50 percent of the amount you should have withdrawn.

IRA sponsors usually withhold 10 percent of your payout as taxes to be sent to the IRS. But if you want to block withholding or have more than 10 percent withheld, tell your IRA sponsor when you request the distribution.

Kimberly Lankford is a contributing editor to Kiplinger's Personal Finance magazine. Send your questions and comments to moneypower@kiplinger.com.