WASHINGTON — An estimated 3 million to 6 million households that file 2014 income tax returns might incur penalties this tax season for failing to secure health insurance last year under the Affordable Care Act.

Senior officials at the Treasury and Health and Human Services departments wouldn’t confirm the estimates during a telephone briefing Wednesday. They did, however, say that 2 percent to 4 percent of an estimated 150 million taxpayers are likely to be penalized.

The health law’s “individual mandate” required last year for the first time that most Americans obtain health insurance or face a penalty equal to 1 percent of their annual household income, or $95 per adult and $47.50 per child – whichever is higher.

The 2015 penalty, which will be levied next year, jumps to 2 percent of income or $325 per person. In 2016, it rises to 2.5 percent of household income or $695 per person.

An estimated 25 percent of personal income-tax filers didn’t have health coverage for all or most of last year, officials said. That’s roughly 37.5 million taxpayers.

Some will face no penalties by claiming any number of exemptions to the coverage mandate based on religious affiliation, immigration status, income and other factors.

In addition, some who received tax credits to help purchase their 2014 marketplace coverage might face a partial or complete loss of their income tax refunds – or end up owing the government money – if the income estimate used to calculate their subsidy is below their 2014 earnings.

It’s unclear how many people might be subject to these financial penalties, but tax credits were distributed to an estimated 3 percent to 5 percent of tax filers last year, officials said. That’s an estimated 4.5 million to 7 million households.

Marketplace plan members were instructed to notify their insurers and HHS when their incomes or life statuses changed so that their tax credits could be adjusted accordingly. Doing so would lessen the likelihood of surprising financial penalties when they filed their income taxes. Changes that could trigger subsidy adjustments include relocation, marriage, a job loss or a large pay raise.

Those who had individual marketplace coverage last year will get a new federal income tax form – 1095-A – that must be filed with their 2014 returns.

The Obama administration is partnering with large tax-preparation businesses and nonprofit organizations to help spread awareness of and answer questions about the new health insurance tax provisions.

Taxpayers with additional questions can contact HHS call centers at 800-318-2596.

While some consumer confusion is inevitable as the tax season swings into high gear, Andy Slavitt, principal deputy administrator at HHS’ Centers for Medicare & Medicaid Services, said the agency was ready for the challenge.

“We’re not going to predict how things are going to go … but we feel as good as we can” about preparations for the upcoming tax season, Slavitt said.