The IRS has announced that the tax season will start on January 19, 2016. To be sure, tax prep is probably the last thing on your mind when you're just trying to survive the holiday shopping frenzy. But if you take a little bit of time now—and use the free tools that tax prep software makers offer online and via mobile—you'll get a much better idea of what you might receive or owe on your taxes next year.

That could be a real help when it comes to filing your return come the opening bell. Early filers have a head start when it comes to getting tax refunds too. Yours might arrive just as you're having to pay those holiday credit card bills.  

If you haven't spoken to a tax professional, the free preview features by tax software companies like TurboTax and H&R Block will give you an idea of what you'll owe. When I recently tried them, I found both relatively easy to use, each taking less than 15 minutes. The refunds they calculated differed by about $200–a margin of less than 10 percent. More important, the process inspired me to think of some moves you could make now before year-end to bulk up your refund even more.

• Increase itemized deductions, including charitable contributions, business expenditures, and qualified medical expenses (bother with that last one only if you're close to or above the threshold at which you can get a deduction: 10 percent of your household adjusted gross income or, for households where one filer is 65 or older, 7.5 percent of AGI).

• Adjust your withholding for the last week of December. Check the IRS's withholding calculator for help.

• Sell investments to harvest losses; you can deduct up to $3,000 in losses and carry over the rest to subsequent years.

• Pay 2016 property taxes due in January before year-end, unless you expect to be subject to the Alternative Minimum Tax. In that case, you won't benefit from that accelerated payment. If you expect to be a victim of the AMT, speak to a tax professional before making any moves.

• If you need to take out required minimum distributions from retirement accounts, donate some or all of that money for an additional tax savings. (That temporary move was made permanent in the budget signed by the President last week.)

Get More Money for College

Another major reason to estimate your taxes early is so you can fill out and submit the Free Application for Financial Aid (FAFSA) with preliminary income figures as soon as the application becomes available on January 4. You can add your real figures later, after you complete your tax returns. Mark Kantrowitz, CEO of MK Consulting and an expert on student financial aid, says his research shows early applicants get more.

Other motivations for planning way ahead: If you owe, you've got more time to figure out how you're going to come up with the money. And if you expect a refund, you'll have more time to dream about how you're going to spend it.