The Affordable Care Act (ACA), officially called the Patient Protection and Affordable Care Act, is the comprehensive health care reform law enacted in March 2010. It reshaped how Americans get and pay for health insurance by creating new marketplaces for buying coverage, expanding Medicaid for low-income adults, and establishing rules that prevent insurers from denying coverage based on your health history. Since the law took effect, the national uninsured rate has dropped from 16% in 2010 to 8.2% as of early 2024.
The Three Core Goals of the ACA
The law was built around three primary objectives. First, it aims to make health insurance affordable for more people by offering subsidies (called premium tax credits) that reduce monthly costs for households within certain income ranges. Second, it expands Medicaid to cover adults with low incomes. Third, it supports new approaches to delivering medical care that are designed to bring down health care costs overall.
In practice, these goals work together. Subsidies help middle-income families afford private plans, Medicaid expansion catches people who earn too little to benefit from those subsidies, and delivery reforms push the system to spend money more efficiently.
How the Health Insurance Marketplace Works
The ACA created Health Insurance Marketplaces, sometimes called “exchanges,” where individuals and small businesses can compare and buy private health plans in one place. Think of it as a regulated shopping site for health insurance. If your state runs its own marketplace, you’ll use that; otherwise, you’ll shop through the federal site at HealthCare.gov.
Plans sold on the marketplace are grouped into metal tiers (Bronze, Silver, Gold, Platinum) based on how they split costs with you. Bronze plans have lower monthly premiums but higher out-of-pocket costs when you need care. Platinum plans cost more each month but cover a larger share of your bills. All marketplace plans must meet minimum coverage standards set by the law.
Pre-Existing Condition Protections
Before the ACA, insurance companies could refuse to cover you, charge you significantly more, or exclude treatment for health problems you already had. The law changed that entirely. Insurers cannot deny you coverage or raise your premiums because of a pre-existing condition like asthma, diabetes, cancer, or pregnancy. They also cannot limit benefits for that condition or refuse to cover treatment once you’re enrolled.
These protections apply to both adults and children. The one exception involves “grandfathered” plans, which are older plans that existed before the ACA was signed and haven’t made certain changes since then. Those plans do not have to follow the pre-existing condition rules.
What Every Plan Must Cover
ACA-compliant plans in the individual and small group markets are required to cover ten categories of essential health benefits:
- Outpatient care: doctor visits and services you receive without being admitted to a hospital
- Emergency services
- Hospitalization
- Maternity and newborn care
- Mental health and substance use treatment, including behavioral health services
- Prescription drugs
- Rehabilitative services and devices
- Lab tests
- Preventive care, wellness visits, and chronic disease management
- Pediatric services, including dental and vision care for children
Before the ACA, many individual plans didn’t cover maternity care, mental health treatment, or prescription drugs at all. The essential health benefits requirement ensures a baseline of coverage regardless of which plan you pick.
Financial Help: Premium Tax Credits
If you buy coverage through the marketplace, you may qualify for a premium tax credit that lowers your monthly bill. Traditionally, this credit was available to households earning between 100% and 400% of the federal poverty level. For 2021 through 2025, Congress temporarily removed the upper income cap, so people earning above 400% of the poverty level can also receive credits if their premiums would otherwise consume a large share of their income.
You can take the credit in advance, meaning it’s applied directly to your monthly premium so you pay less out of pocket each month. Or you can claim the full credit when you file your taxes. If your income changes during the year, you may owe some of the advance credit back or receive a larger refund, so it’s worth updating your marketplace application when your income shifts.
Medicaid Expansion
The ACA originally intended for every state to expand Medicaid to cover all adults earning up to 138% of the federal poverty level, which works out to about $21,597 for an individual in 2025. The Supreme Court ruled in 2012 that states couldn’t be forced to expand, making it optional. As of now, 41 states (including Washington, D.C.) have adopted the expansion, while 10 states have not.
In states that haven’t expanded, adults without children often can’t qualify for Medicaid at all, no matter how low their income is. And if they earn too little to qualify for marketplace subsidies, they fall into what’s known as the “coverage gap,” where neither program helps them. This gap affects residents of non-expansion states and is one of the law’s most debated shortcomings.
Coverage for Young Adults Under 26
One of the ACA’s most widely used provisions allows young adults to stay on a parent’s health insurance plan until they turn 26. This applies even if you’re married, have children, live on your own, aren’t claimed as a tax dependent, or have access to coverage through your own job. If you’re on a parent’s marketplace plan, coverage continues through December 31 of the year you turn 26.
This rule applies to job-based plans that cover dependents and to marketplace plans. If a parent pays the full cost of a marketplace plan without receiving a tax credit, you can be included on their plan even if they don’t claim you as a tax dependent.
The Individual Mandate Today
When the ACA was first implemented, it included a federal penalty for people who went without health insurance, commonly called the “individual mandate.” Congress reduced that federal penalty to $0 starting in 2019, so there is no longer a federal fee for being uninsured.
A handful of states have enacted their own mandates, though. If you live in one of those states and go without coverage, you could face a state-level fee when you file your state taxes. Checking your state’s specific rules is the simplest way to know if this applies to you.
How and When to Enroll
Marketplace enrollment follows a yearly schedule called Open Enrollment. For coverage starting January 1, Open Enrollment begins November 1 and runs through January 15. If you enroll or change plans by December 15, your new coverage starts January 1. If you enroll between December 16 and January 15, coverage starts February 1. After Open Enrollment closes, you can only sign up or switch plans if you experience a qualifying life event.
Qualifying life events include losing other health coverage, moving to a new area, getting married, having a baby, or adopting a child. These events trigger a Special Enrollment Period, typically lasting 60 days, during which you can sign up for a marketplace plan outside the regular window. Medicaid and the Children’s Health Insurance Program (CHIP) have no enrollment window; you can apply year-round.