In 2016, the first wave of baby boomers turned 70½, and many more reach that milestone in 2017 and 2018. What's so special about 70½? That's the age when you must begin taking required minimum distributions (RMDs) from tax-deferred retirement accounts, including traditional IRAs, SIMPLE IRAs, SEP IRAs, SARSEPs, and 401(k), 403(b), and 457(b) plans. Original owners of Roth IRAs are not required to take RMDs.

If you're still employed (and not a 5% owner), you may be able to delay minimum distributions from your current employer's plan until after you retire, but you still must take RMDs from other tax-deferred accounts (except Roth IRAs). The RMD is the smallest amount you must withdraw each year, but you can always take more than the minimum amount.

Failure to take the appropriate RMD can trigger a 50% penalty on the amount that should have been withdrawn - one of the most severe penalties in the U.S. tax code.

Distribution deadlines

Even though you must take an RMD for the tax year in which you turn 70½, you have a one-time opportunity to wait until April 1 (not April 15) of the following year to take your first distribution. For example:

• If your 70th birthday was in May 2017, you turned 70½ in November and must take an RMD for 2017 no later than April 1, 2018.
• You must take your 2018 distribution by December 31, 2018, your 2019 distribution by December 31, 2019, and so on.

IRS tables

Annual RMDs are based on the account balances of all your traditional IRAs and employer plans as of December 31 of the previous year, your current age, and your life expectancy as defined in IRS tables.

Most people use the Uniform Lifetime Table (Table III). If your spouse is more than 10 years younger than you and the sole beneficiary of your IRA, you must use the Joint Life and Last Survivor Expectancy Table (Table II). Table I is for account beneficiaries, who have different RMD requirements than original account owners. To calculate your RMD, divide the value of each retirement account balance as of December 31 of the previous year by the distribution period in the IRS table.

Aggregating accounts

If you own multiple IRAs (traditional, SEP, or SIMPLE), you must calculate your RMD separately for each IRA, but you can actually withdraw the required amount from any of your accounts. For example, if you own two traditional IRAs and the RMDs are $5,000 and $10,000, respectively, you can withdraw that $15,000 from either (or both) of your accounts.

Similar rules apply if you participate in multiple 403(b) plans. You must calculate your RMD separately for each 403(b) account, but you can take the resulting amount (in whole or in part) from any of your 403(b) accounts. But RMDs from 401(k) and 457(b) accounts cannot be aggregated. They must be calculated for each individual plan and taken only from that plan.

Also keep in mind that RMDs for one type of account can never be taken from a different type of account. So, for example, a 401(k) required distribution cannot be taken from an IRA. In addition, RMDs from different account owners may never be aggregated, so one spouse's RMD cannot be taken from the other spouse's account, even if they file a joint tax return. Similarly, RMDs from an inherited retirement account may never be taken from accounts you personally own.

Birthday Guide: This chart provides sample RMD deadlines for older baby boomers.

Even if you're generally comfortable with your finances, you may occasionally worry about how much you're spending, especially if you consistently have trouble saving for short- or long-term goals. Here are a few questions to ask that might help you decide whether a purchase is really worth it.

Why do I want it?

Maybe you've worked hard and think you deserve to buy something you've always wanted. That may be true, but are you certain you're not being unduly influenced by other factors such as stress or boredom?

Take a moment to think about what's important to you. Comfort? Security? Safety? Status? Quality? Thriftiness? Does your purchase align with your values, or are you unconsciously allowing other people (advertisers, friends, family, neighbors, for example) to influence your spending?

How will buying this now affect me later?

When you're deciding whether to buy something, you usually focus on the features and benefits of what you're getting, but what are you potentially forgoing? When you factor this into your decision, what you're weighing is known as the opportunity cost. For example, let's say you're trying to decide whether to buy a new car. If you buy the car, will you have to give up this year's family vacation to Disney World? Considering the opportunity cost may help you evaluate both the direct and indirect costs of a purchase. Ask yourself how you will feel about your purchase later. Tomorrow? Next month? Next year?

Will this purchase affect your family?

Couples often fight about money because they have conflicting money values. Will your spouse or partner object to your purchasing decision? And what about your children? Children learn from what they observe. Are you comfortable with the example you might be setting?

Do I really need it today?

Buying something can be instantly and tangibly gratifying. After all, which sounds more exciting: spending $1,500 on the ultra-light laptop you've had your eye on or putting that money into a retirement account? Consistently prioritizing an immediate reward over a longer-term goal is one of the biggest obstacles to saving and investing for the future. The smaller purchases you make today could be getting in the way of accumulating what you'll need 10, 20, or 30 years down the road.

Be especially wary if you're buying something now because "it's such a good deal." Take time to find out whether that's really true. Shop around to see that you're getting the best price, and weigh alternatives. You may discover a lower-cost product that will meet your needs just as well. If you think before you spend money, you may be less likely to make impulse purchases and more certain that you're making appropriate financial choices.

Can I really afford it?

Whether you can afford something depends on both your income and your expenses. You should know how these two things measure up before making a purchase. Are you consistently charging purchases to your credit card and carrying that debt from month to month? If so, this may be a warning sign that you're overspending. Reexamining your budget and financial priorities may help you get your spending back on track.