(Bloomberg) — About 6.6 million U.S. taxpayers paid a penalty imposed for the first time this year for not having health insurance, about 10 percent more than the Obama administration had estimated — though a portion didn’t need to.

The penalty of as much as 1 percent of income was implemented under the Patient Protection and Affordable Care Act, and was meant to encourage people to sign up for health insurance. The Treasury Department had said in January that as many as 6 million taxpayers would pay the fine.

The average penalty was $190, the National Taxpayer Advocate, the in-house ombudsman of the Internal Revenue Service, said Wednesday in a report. About 300,000 taxpayers overpaid the penalty by a total of $35 million. Most should have been exempt for their low income, according to the agency.