To err is human, but some mistakes are worse than others, and slip-ups that occur while you're planning for retirement can come back to haunt you financially.

But it may not be too late for you to fix some common mistakes. Here are five prime examples:

1. Saving too little. It seems obvious, but not setting aside enough money could become a big problem if you underestimate the amount you'll need to live on—all the more likely as life expectancies continue to rise. So if your employer offers a 401(k) plan with matching contributions, try to take full advantage of it, even though your take-home pay will be reduced by deferrals. And you can supplement these savings with IRA contributions.