Your 2012 federal income tax return holds special significance this year.

That's because the return will be the main tool used to determine whether you're eligible for federal assistance to buy health insurance through state-based insurance exchanges that will open next year.

This is all part of the federal Affordable Care Act, which takes full effect in 2014. Most Americans will be required to buy health insurance or face a tax penalty.

The new law provides two forms of federal subsidies to help pay for health insurance provided by the exchanges.

Each state will have its own exchange serving people who buy their health insurance directly, as well as a separate one for small businesses. The vast majority of people now covered by employer plans will not see a change.

And make no mistake: The insurance exchanges are coming to every state, even those led by staunch Republican opponents of the health care overhaul. In a number of states, the exchanges will be operated by the federal government, over state opposition.

The first type of subsidy offered will be a monthly premium-assistance tax credit that will lower the amount an individual or family must pay. The tax credit will be sent directly to your insurance company and applied to your premium, so you pay less out of your own pocket.

"You will pay a percentage of your income as your share of the premium, and the federal government will pay the rest," said Brian Haile, senior vice president for health policy at Jackson Hewitt Tax Service. "The percentage that you pay will depend on your household size and your income."