The Affordable Care Act’s biggest year is, without a doubt, 2014: That’s when the federal subsidies to purchase health insurance roll out. It’s also when penalties for not buying coverage kick in.

But many of the big changes will start gradually in 2013. They range from increasing payments to Medicaid doctors to upping Medicare taxes to the first open-enrollment period for health insurance exchanges. Here’s a guide to what will happen this year.

1. Growth in health care costs will slow to a new low.

The United States is expected to spend $2.9 trillion on health care in 2013, according the Centers for Medicare and Medicaid Services. That would be 3.8 percent more than the $2.8 trillion that CMS estimates we spent in 2012.

That growth rate would be the slowest health care growth in decades. That has little to do with the Affordable Care Act, the CMS actuaries explain, and a lot more to do with slow income growth. “Consumers are expected to remain sensitive to rising health costs, particularly given continued low projected income growth,” they write. “In this environment, consumers are likely to continue to be judicious in their use of health-care services.”

2. Your Medicare taxes will increase.

Two new taxes to finance Medicare are meant to bring in additional revenue to continue funding the health care program for seniors.

Employers already take out 7.65 percent of workers’ wages to support the elderly and the disabled. Of that, 1.45 percent goes toward paying Medicare’s hospital bills. Obamacare increases the Medicare hospital tax by 0.9 percent, beginning in 2013, for anyone who earns more than $200,000 ($250,000 for joint filers). It also creates a 3.8 percent tax on investment income, setting income thresholds at the same $200,000 and $250,000 levels. Taken together, those two provisions are expected to generate $210.2 billion over the next decade.

3. Your insurance plan will be explained in plain English.

Say goodbye to insurance forms with eight-point font that stretch on for dozens of pages. Starting in 2013, the Affordable Care Act requires insurance companies to send subscribers a standardized, four-page summary of benefits and coverage that runs through the health plan in easy-to-understand terms. Think of this as a nutrition label for health insurance.

This requirement started a few months ago: Health insurance plans with open enrollment periods after Sept. 23 were required to offer this information. For anyone buying insurance from a plan with earlier open enrollment, these summaries will show up for the first time in 2013.

4. Primary care providers in Medicaid will get a 73 percent raise on average.

The Congressional Budget Office estimates Medicaid will gain 7 million enrollees in 2014, as a result of the health law expanding the program to up to 133 percent of the poverty line.

The federal government wants to make sure doctors keep serving that population, even though Medicaid tends to pay physicians less than private insurance. That’s why the health care law includes a provision that boosts reimbursements in Medicaid to match those of Medicare for 2013 and 2014. On average, that will mean a 73 percent raise for Medicaid doctors, according to researchers at the Urban Institute.

5. The exchanges will open for business.

We often talk about Jan. 1, 2014, as the date states need to be ready for the health law. But when you talk to the states actually working to roll out the law, they often talk about Oct. 1, 2013, as a much more significant deadline. That’s the day the health exchanges open for business, when any American can go online, compare plans and, if desired, purchase health insurance.

This is true for state-operated health exchanges as well as those being run by the federal government.