The court also declined to strike down a portion of the law that would extend Medicaid to more low-income families, up to 1.33 times the current poverty level.
The mammoth law contains many interconnected provisions, so the impact of the court's ruling will vary greatly by family circumstance.
For the roughly 50 million uninsured Americans, the court's ruling has the biggest implications. For the majority of citizens who currently have insurance, the ruling could mean some important changes as well, such as to their health plans or their personal tax rates.
Many less affluent Americans who do not qualify for Medicaid may now gain health coverage as the program is expanded.
For others among the ranks of some 50 million uninsured Americans, the law creates a system of tax subsidies – designed to help more Americans afford health coverage – plus the mandate to buy insurance or pay a fine.
Consider a working-age family of four, with an income of $60,000 and no earner covered by an employer-based health plan.
According to a "health reform subsidy calculator" created by the Kaiser Family Foundation, which tracks U.S. health-care policies, this family would reap a tax subsidy of $9,308 if they buy insurance in 2014. That would cover most of a total premium cost of $14,245, perhaps putting health insurance within the family's financial reach.
Without the "stick" of an individual mandate, this "carrot" might not prompt as many households to fully insure themselves. To take the family in the example just given, they would still face a sizable premium (nearly $5,000), plus the prospect of additional out-of-pocket expenses, capped for this family at $6,250.
For comparison, the typical U.S. household in 2010 had total spending of $48,109, with $3,157 of that for health care, according to a survey by the U.S. Labor Department.
The law provides for people who don't have an employer-based plan to shop for insurance on "exchanges" set up at the state level, with coverage plans ranging from "bronze" to "platinum." The Kaiser Family Foundation's calculator focuses on the cost of a "silver" plan, and the example given above assumes the household is headed by a 45-year-old.
Note this: The subsidies are designed to phase out as household income rises, so the family of four would see the cost of health-insurance jump once their income exceeds about $93,700 – making them ineligible for federal subsidies.
Some will remain uninsured
Even with the Supreme Court's ruling to uphold the law, many Americans are likely to remain uninsured.
As the Kaiser Family Foundation explains, some citizens would be exempt from the mandate (such as for religious reasons, being in prison, being an undocumented immigrant, or not being able to afford insurance). The law deems insurance to be unaffordable for people when insurance premiums after subsidies and employer contributions exceed 8 percent of family income.