Big changes to note
Home office deduction rules: Starting with the 2015 tax year, those who qualify to claim a home office deduction can elect to use a new simplified calculation method; under this optional method, instead of determining and allocating actual expenses, the square footage of the home office is simply multiplied by $5. There's a cap of 300 square feet, so the maximum deduction under this method is $1,500. Not everyone can use the optional method, and there are some potential disadvantages, but for many the new simplified calculation method will be a welcome alternative.
Same-sex married couples: Same-sex couples legally married in jurisdictions that recognize same-sex marriage will be treated as married for all federal income tax purposes, even if the couple lives in a state that does not recognize same-sex marriage. If this applies to you, and you're legally married on the last day of the year, you'll generally have to file your federal income tax return as a married couple--either married filing jointly, or married filing separately. This affects only your federal income tax return--make sure you understand your state's income tax filing requirements.
More health-care reform changes take effect in 2016: Beginning in 2016, you'll generally be required to have adequate health-care coverage or face a penalty tax (a number of exceptions apply). A new premium tax credit will also be available to qualifying individuals.