Hold somebody’s hand when you cross the street. Don’t chew with your mouth open. Be nice to the other kids at recess. Ever since you started crawling, you’ve had rules all around you—you think somebody would let up when retirement rolled around! But, no, that’s not the case, and so as you prepare now for retirement, you need to know about 401k rules.

The biggest of the 401k rules to know are the contribution limits. When you are contributing to your 401(k), as of 2009 you’re allowed to max out at $16,500. The thing about that limit is that it isn’t equally applicable to multiple accounts. If you do have more than one 401(k) plan, you’re only allowed $16,500 to spread between the two or however many you have. Three 401(k)s aren’t going to get you a $39,500 contribution limit. However, if you’re self-employed, the limit jumps to $49,000—and that’s really nice, because since it’s pre-tax income, that drops your tax bracket significantly. (Even if you’re not self-employed, it’s still pre-tax income.)

Also important among the contribution 401k rules is the fact that after 50 you’re allowed to make catch-up contributions. As of 2009, you are permitted to make $5,500 in contributions on top of your $16,500. This is to let you pay yourself back for those days in your youth when you were making $25,000 per year and putting $201.35 into your 401(k) every Christmas as a gift to yourself. The nice thing about these limits is that they don’t include employer matching contributions or profit-sharing plans tied to your 401(k). If you pay your full $16,500 and your employer has a contribution matching policy of six percent, that $990 goes right in on top of your full contribution, no questions asked.

Without doing something illegal, there’s no way around those particular 401k rules. Some rules, however, are employer-specific, so you can wriggle around the details at times. For example, some employers permit you to take a loan against your 401k (a highly viable strategy if you need the cash now but don’t want to suffer a hit from taxes just yet); some won’t. Others provide for contribution matching, as we mentioned; yet others don’t. Among those that do, of course, there are differences in how much they match (generally, though, you won’t find it much above 6%). Those might be rules for the employer more than for you, but they’re still important rules to know.

Wriggling around those employer-specific rules comes into play when you look at the rollover rules for your 401k. If you change jobs, you can sometimes hold onto both accounts (which may or may not be advisable, depending); sometimes, though, one employer or the other forbids that (though you should usually try not to cash out your stock too early if stock is part of your 401k). Some 401k rules may seem to be a headache as you consider some of this wriggling you may have to do, but others may actually be strongly to your benefit. Whatever the case, make sure you know the rules and play by the rules—that much, at least, hasn’t changed since you had to be nice to the other kids at recess.