And the IRS wants these taxpayers to lighten their retirement reserves soon. April 1, to be exact.

If you turned 70½ last year and haven't yet started spending what Uncle Sam thinks you should, on April 1 you have to take an IRS-specified amount out of your retirement account, even if you're still working.

This withdrawal, known as a required minimum distribution, must come out of retirement savings where taxes have been deferred. This includes several popular IRAs -- traditional, simplified employee pension, or SEP, and SIMPLE accounts -- as well as certain employer-sponsored plans.

It's no secret why the IRS wants you to start drawing down these accounts. Your money has been sitting there for years, tantalizingly out of reach of the tax collector as it accrued tax-deferred earnings.

Why withdraw?
You don't care what the rules are. You don't need the money, you don't want to pay taxes on any withdrawals, and you're leaving your account untouched. Not a good idea.

The IRS will hit you with an excess accumulation tax. This levy is 50 percent of the required distribution that you didn't take. For example, you didn't withdraw the required $1,000 from your traditional IRA. The tax charge for your defiance is $500. For a taxpayer in the 25-percent income tax bracket, that's twice what you would have paid in taxes if you'd simply followed the distribution rule.

If you can convince the IRS that your distribution shortfall was due to "reasonable error" and that you're taking steps to rectify the situation, the agency could waive the penalty. In that case, file Form 5329, go ahead and pay the excess accumulation tax, and attach a letter of explanation. If the IRS agrees that you shouldn't be penalized, it will refund the excess tax.

Determining your distribution
OK, you've accepted that you must start siphoning off your retirement fund. Just how much do you have to withdraw? That depends.

The IRS has created three tables based on life expectancies to figure the minimum withdrawal amount, which is a percentage of your IRA based on your age.

• Retirement-plan beneficiaries use the first table.
• Married account owners with spouses more than 10 years younger use the second table. Since its calculations incorporate the younger age of the spouse to spread withdrawals over a longer life expectancy, you don't have to take out as much.
• Most account holders use table three, known as the Uniform Lifetime Table. It is for singles and married savers with spouses closer to their own ages.