WASHINGTON (AP) — The tax filing season is getting off to a later start, thanks to last year's government shutdown. When they begin preparing their returns, higher-income taxpayers will find a new top tax rate, higher Medicare taxes and the phase-out of deductions and exemptions. Legally wed same-sex couples may be subject to the so-called marriage penalty. All taxpayers, meanwhile, will have a harder time qualifying for medical deductions. For those working at home, there's a simplified formula for figuring the home office deduction. Many provisions for the 2013 tax year were set early. The alternative minimum tax was patched permanently to prevent more middle-income workers from being drawn in. Similarly, tax rate tables and the standard deduction were adjusted for inflation. The Internal Revenue Service will begin accepting tax returns Jan. 31.