Although the vast majority of households — about 120 million of them — were able to start filing Jan. 30, some people with more complex tax issues won’t be able to start filing until later this month or March because of additional changes the IRS needs to make based on the fiscal-cliff deal.

That group includes filers using more than two dozen forms to claim specialized-tax credits, such as those for alternative-fuel vehicles, residential-energy equipment, depreciation of property and several other business-related provisions, the IRS said.

The agency will announce when it will start accepting those tax forms soon.