Q. I started a new job that offers a 457 retirement plan rather than a 401(k). Are the rules the same?

A. The private-sector 401(k) and the 457 plan for public-sector employees have a lot in common. Both retirement-savings plans let you set aside pretax money (up to $17,500 in 2013) in mutual funds -- in other words, your contributions aren't reported to the IRS as taxable income so you don't pay taxes until you take withdrawals in retirement. Some employers also offer Roth versions of these plans, in which your contributions are not tax-deductible but the money is tax-free when withdrawn in retirement.

But there are a few key differences. The biggest is that after you leave your job you can withdraw money from a 457 without penalty no matter how old you are. With a 401(k), you can withdraw money without penalty only if you're 55 or older in the year you leave the job. That means it's a good idea to keep your money in the 457 after you leave, rather than rolling it into an IRA, if you think you'll want access to the money before age 59 1/2. If it's in an IRA, withdrawals before 59 1/2 are subject to a 10-percent penalty.

As with 401(k)s, 457 plans permit extra catch-up contributions. You can boost contributions by $5,500 a year starting the year you turn age 50 -- bringing your total limit to $23,000 for 2013. Or you can take advantage of a special catch-up opportunity available just for 457s. If you're within three years of the "normal retirement age" specified in the plan documents (often the age when you can collect unreduced benefits in your pension plan, which is age 60 for many employees and in the fifties for some public-safety workers), you may contribute as much as double the maximum for those three years if you haven't maxed out your contributions in the past. This extra catch-up option can be helpful if you're getting a big payout from sick and vacation days right before retirement and would like to invest more pretax money.

(Kimberly Lankford is a contributing editor to Kiplinger's Personal Finance magazine and the author of Ask Kim for Money Smart Solutions (Kaplan, $18.95). Send your questions and comments to moneypower@kiplinger.com. And for more on this and similar money topics, visit http://www.Kiplinger.com.)