The Affordable Care Act's biggest year is, without a doubt, 2014 - when federal subsidies to buy health insurance roll out and penalties for not buying coverage kick in. But many of the big changes will start gradually this coming year. Here's a quick guide:

1Growth 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 to actuaries at the Center for Medicare and Medicaid Services (CMS). That would be 3.8 percent more than the $2.8 trillion the CMS estimates we spent in 2012. That 3.8 percent growth rate, if it actually happens, 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.

2Medicare taxes will increase. Two new taxes 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 disabled. Of that, 1.45 percent goes toward Medicare's hospital bills. The act 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 mentioned above. Taken together, those two provisions are expected to generate $210.2 billion over the next 10 years.

3Say goodbye to insurance forms with tiny type that stretch on for dozens of pages. Starting in 2013, the Affordable Care Act requires insurers to send their subscribers a standardized, four-page summary of benefits and coverage in easy-to-understand terms.

4Primary-care providers in Medicaid will get a 73 percent raise. The Congressional Budget Office estimates that Medicaid will gain 7 million enrollees in 2014, as a result of the health law expanding the program people making about 130 percent of the poverty line. The government wants to make sure doctors keep serving that population, even though the Medicaid program tends to pay physicians less than private insurance. That's why the health care law includes a provision that boosts primary care reimbursements in Medicaid to match those of Medicare for 2013 and 2014.

5The exchanges will open for business. We often talk about Jan. 1, 2014, as the date that states need to be ready for the health reform 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 when the health exchanges open for business, when any American can go online, compare plans and, if they want, purchase health insurance.