The 2013 calendar year may be over, but opportunities to lower last year's tax liability are not.
Indeed, while many of the most common tax-planning strategies used to accelerate income or defer deductions—including tax-loss harvesting, prepaying medical expenses and managing your year-end bonus—had to be implemented by Dec. 31, others remain ripe for the picking. If you know where to look.
"In a year where tax rates are higher and the 3.8 percent surtax on net investment income will affect higher-income individuals, any deductions you can find will be worth even more," said Bill Dendy, a certified financial planner and president of Elite Financial Management in Dallas.
Effective this filing season, the new top tax rate for individuals making more than $400,000 ($450,000 if you're married filing jointly) is 39.6 percent. Those with modified adjusted gross income of at least $200,000 ($250,000 for married taxpayers) will also be subject to a 0.9 percent Medicare tax and/or the net investment income surtax of 3.8 percent on unearned income.
Dendy's advice to clients? Revisit your tax-planning strategy, and don't leave any deductions on the table.
Taxpayers have between now and April 15 to make prior-year contributions to their traditional and Roth IRAs, along with their Health Savings Account (HSA).
Contribution limits to your IRA are $5,500 for 2013, but the tax-deduction benefit starts phasing out for married taxpayers filing jointly with an adjusted gross income of more than $181,000 and single filers who earn more than $114,000.
Likewise, taxpayers who made less than the $3,250 maximum contribution to their HSA last year may still make prior-year contributions until April 15. HSAs, which must be paired with a high-deductible health insurance plan, are medical savings accounts that are funded with pretax dollars. The earnings become tax-free if used for qualified medical expenses, and any unused money in the account can be used to cover out-of-pocket health-care costs in retirement.
Maximize IRA contributions
Small-business owners and the self-employed have one other tool at their disposal: the SEP-IRA, which can also be funded for the prior year through April 15.
Contribution limits for SEP IRAs in 2013 are the lesser of 25 percent of your total compensation, or $51,000, according to the IRS, but the degree to which those contributions are deductible depends on IRS income tables and a worksheet.
It's worth noting that self-employed individuals who obtain an extension for filing their return can actually delay their SEP contribution further still, giving them until the end of the extension period (Oct. 15) to actually deposit the money, said Christopher Olsen, a certified financial planner with Ameriprise Platinum Financial Services in Lodi, Calif.
"Effectively, you have through Oct. 15 of this year to fund your SEP for 2013," he said. "It's a lot more flexible than a regular IRA or a Roth because it gives individuals who know they have some big check coming in later this year the chance to make a backward contribution."
Just remember that an extension to file does not mean you can delay the payment of any income tax you may owe. It merely waives the penalty for late filing, which is 5 percent of your unpaid tax bill every month that your return is late, up to a maximum of 25 percent. You'll still owe a 0.5 percent penalty if you file on time but pay late.
Take advantage of new home-office deductions
If you use part of your home for business, you may also be able to take advantage of the new, simplified calculation for claiming a home-office deduction in tax year 2013, said Dendy.
In years past, you had to measure the actual expense of your home office, including mortgage interest, insurance, utilities, repairs and depreciation, but the new, simplified option allows you to take a standard deduction of $5 per square foot of the portion of your home used for work.
"It's a lot easier, because you don't have to keep all those records," Dendy pointed out. "Most people didn't even want to claim their home office, because they viewed it as an audit trigger, but those who can take that deduction should make sure they do it this year."
(Read more: 7 tech tools to make tax prep less frustrating)
Troll for tax credits
Taxpayers should also troll for miscellaneous tax credits that can not only reduce the amount of federal tax they owe but potentially even result in a refund. "Look back over your receipts to see if you bought anything that would apply for an energy-efficient tax credit," said Dendy, noting credits are far more valuable than write-offs, as they reduce your taxes dollar for dollar.
The government provides a list of Energy Star appliances that are eligible for a tax credit, along with a list of the hybrid or electric vehicles that qualify for a tax credit of up to $7,500.
If you or your kids are in college, you may also be able to offset some of the expense by claiming either the American Opportunity Tax Credit (AOTC) or the Lifetime Learning Credit (LLC), but not both.
The AOTC allows taxpayers with modified adjusted gross income of less than $180,000 a credit of up to $2,500 for education expenses paid for each student, while the LLC provides a credit of up to $2,000 for qualified education expenses paid for any eligible student, including yourself, your spouse or a dependent for whom you claim an exemption on your tax return.
(Read more: How to keep IRS auditors at bay)
Staying organized as you prepare your 2013 taxes can also save you money, not only because it helps identify deductions but also because it will ensure you file an accurate return, said Greg Hammond, a certified financial planner with Kelly Financial Group in Wethersfield, Conn.
"Taking steps now to organize your financial and tax records can make the tax process easier," he noted. "Over the next few weeks, take a look at your credit card bills and bank statements to spot possible charitable contributions that you made throughout the year that can easily be overlooked."
Keep your W-2s and 1099s in a central location, too, so they don't have a chance to walk away, which could force you to file an incomplete or late return.
"I see that occasionally with my own clients who misplace a 1099 for an investment account, and transactions that occurred in that account don't get reported," said Hammond. "They get a surprise in a few years when the IRS catches up with them."
There's much you can do between now and April 15 to lower your 2013 tax bill. By taking advantage of prior-year contributions and claiming all credits and deductions for which you are eligible, you can cut your taxable income down considerably and potentially keep more of your hard-earned money.
—By Shelly K. Schwartz, Special to CNBC.com