The double nickel year has potential for allowing you to tap your 401(k) without an early withdrawal penalty, but you have to know exactly how it works to avoid problems.
There's one exception to the rule that you must be at least 59 ½ to tap your 401(k) without incurring a 10% early-withdrawal penalty, but you have to tread carefully. If it is the year you turn 55 or older and you leave your job, there's no penalty. You will still owe tax on the withdrawal—a $10,000 payout at a 25% tax rate will still cost you $2,500. There's no free lunch, even here. But, the good news is you don't get hit with a $1,000 early withdrawal penalty.
It doesn't matter how you separate from service. In fact, retiring, being laid-off or even termination will spare you the penalty. Provided you're 55 by the end of the year you leave the job, the rule applies, says the Kiplinger's article, "When You Can Tap a 401(k) Early With No Penalty."