If your company offers a 401(k) or similar retirement savings account, put as much money as you can into it, especially if your employer matches or contributes to the plan as well. Most contributions are made pretax, which means the IRS won't tax you on as much income. For most plans, you can modify your contributions at any time, so as it nears the end of each calendar year, check with your plan administrator to see if you've maxed out your contributions -- and if you haven't, do so. Maximum contributions vary depending on the type of plan and your age [source: IRS Retirement].
There is another workplace account, however, that you probably don't want to leave any money in at the end of the year: a medical flexible savings account (FSA). The Affordable Care Act lowered the annual contribution limit to this type of account to $2,500, so you may not have much or any left at year-end. Check with your administrator or review your account to be sure.
The U.S. Treasury has also changed the rules so that it's possible to carry over $500 to the next year, but your employer must sign up for this benefit. Again, check with your plan administrator. If yours is a use-it-or-lose-it account and you have money left at the end of the year, it will vanish into a stream of bureaucratic procedures, never to be seen again [source: Bell].