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Simple desk calendar for March 2017
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This year, taxpayers have a few extra days to file their returns. But a critical date for some retirees is effectively pushed forward.

First, the big change that affects taxpayers of all ages: The usual April 15 deadline for filing your income tax return is delayed to April 18. That's a fluke of the calendar, involving a holiday celebrated only in Washington D.C. and the fact that April 15 falls on a Saturday.

The other change, for older taxpayers, has to do with the deadline for taking an initial required minimum distribution (RMD) from a tax-advantaged savings account. The deadline is April 1. But because that date falls on a Saturday, investors who need to sell securities in their accounts in order to make a withdrawal need to get that done the day before, Friday March 31. (You may still be able to withdraw cash on Saturday.)

This is no small matter. Anyone who turned 70½ in 2016 and holds assets in a traditional IRA or (in most cases) a 401(k) plan must begin taking distributions. (You may be able to hold off on a 401(k) RMD if you are still working at that employer.)

The penalty for messing up an RMD is stiff: Miss the deadline and you forfeit half the amount you were required to withdraw. Few people miss this deadline on purpose, research shows. It's usually due to procrastination and forgetfulness, or a clerical error of some sort.

This is a confusing deadline because every year after the initial distribution you must take your RMD by Dec. 31. Only in the first year do you get a grace period that runs to April 1 of the following year. And remember that taking an initial distribution now for 2016 means you must take another distribution--for 2017--by Dec. 31 of this year.

Millions of account holders cut it close on this deadline every year, and thousands miss it. Some 43% of Fidelity account holders due for their first RMD in 2016 had not taken the full amount as of Dec. 23. Some 40% had not taken anything, Fidelity reports.

Two-thirds of IRA holders put off taking any distributions until the age they are required to do so, Investment Company Institute data show. That means a lot of folks are likely bumping up against this effective March 31 deadline. It may be extra easy to overlook this date, given that income tax returns need not be filed until April 18 this year.

A 2010 report by the Treasury Department's Treasury Inspector General for Tax Administration estimated that as many as 250,000 IRA owners each year miss the deadline for RMDs totaling $350 million. That tardiness generates potential tax penalties of $175 million.

The government requires distributions to keep individuals from avoiding income tax indefinitely. If you are required to take a distribution, your IRA or 401(k) custodian probably sent you a notice. If not, you should contact them immediately and ask for the calculation, which is based on a drawdown rate designed to get near a zero balance in the last year of your remaining life expectancy.

Going forward, consider automating the process—most IRA and plan administrators will calculate your annual RMD and send you a check quarterly or yearly. Automating your RMDs works best if you have all your tax-deferred savings in one place, which is a strong argument for consolidating your accounts. If you have multiple IRAs, your RMD is based on your total holdings but you can take the dollars from whichever IRA or IRAs you choose.

If you don't need to spend the money you withdraw right away, it makes sense to reinvest it. You can cash out the required amount and stash it in a taxable account. Or if you want to keep your portfolio intact, you may be able to transfer the investments directly to a taxable account, which will save you the hassle of selling and repurchasing the holdings. Either way, of course, you will have to pay the taxes owed.

CORRECTION: An earlier version of this article stated incorrectly that the official IRS deadline for taking certain RMDs had been moved forward to March 31.