How the ACA works and why premiums are rising

Your premium went up, or your coverage suddenly costs more than you expected, and you're trying to figure out why. The Affordable Care Act — the ACA, sometimes called Obamacare — is supposed to make insurance more affordable, so what happened? The honest answer is that the ACA has several interlocking mechanisms designed to keep costs down, and when any one of them weakens or disappears, the effect on your bill can be dramatic. This article explains how those mechanisms work, what has changed over time, and why any of it affects what you actually pay.

The ACA's Basic Structure: What It Actually Does

The ACA did not create a single government insurance program. Instead, it created rules for private insurance companies and built a marketplace — healthcare.gov and state-run equivalents — where individuals and families can shop for coverage. Most Americans are still covered through an employer, Medicare, or Medicaid. The ACA marketplace serves people who don't have access to those options: self-employed people, part-time workers, and others buying insurance on their own.

Plans on the marketplace are grouped into metal tiers — Bronze, Silver, Gold, and Platinum — based on how costs are split between you and the insurer. Bronze plans have lower monthly premiums but higher out-of-pocket costs; Platinum plans have higher premiums but lower costs when you actually use care. Silver sits in the middle and, as you'll see, plays a special role.

How Subsidies Work — and Why They're Easily Misunderstood

The ACA created two separate tools to make coverage more affordable. Understanding the difference between them is essential, because confusing them is the source of most premium shock.

Premium Tax Credits: Reducing Your Monthly Bill

A premium tax credit — often called a subsidy — is money the federal government pays toward your monthly insurance premium. Your subsidy amount is calculated based on your income relative to the Federal Poverty Level (FPL), a figure the government updates annually. The lower your income relative to the FPL, the larger your subsidy. As your income rises, the subsidy shrinks.

Here's a concrete example. Say the benchmark Silver plan in your area costs $550 per month. You're a single adult earning $32,000 per year, which puts you at roughly 240% of the FPL. Based on that income, the ACA says you should pay no more than about 8% of your income toward the benchmark premium — roughly $213 per month. The subsidy covers the gap: $550 minus $213 equals a $337 monthly tax credit. You pay $213. The government pays $337 directly to your insurer.

Now here's the critical thing most people miss: the plan's premium didn't change. Your subsidy did. If your income goes up the following year — a raise, a freelance contract, selling something at a profit — your subsidy may shrink or disappear entirely. Your insurer didn't raise your price. The government's contribution went down. The result looks the same on your bank statement, but the cause is completely different. If your subsidy recently expired or changed, see our companion guide on ACA subsidy expiration for what to do next.

The Income Cliff: A Known Design Problem

Subsidies phase out as income rises, and the phase-out isn't always smooth. People whose income sits just above the subsidy eligibility threshold can face premiums that consume a much larger percentage of their income than people just below it. This is a documented design flaw, not a billing error or a mistake on your application. You may qualify for a subsidy one year and lose it the next due to a modest income change, with a dramatic effect on your cost.

Cost-Sharing Reductions: Lowering Your Deductible and Out-of-Pocket Costs

The second affordability tool is cost-sharing reductions, or CSRs. CSRs lower the out-of-pocket costs you face when you actually use your insurance — things like deductibles, copays, and the maximum amount you'd pay in a year.

CSRs are only available on Silver plans, and only if your income is at or below 250% of the FPL. The lower your income within that range, the more generous the reduction. Someone at 150% FPL on a Silver plan might have a deductible of a few hundred dollars rather than several thousand. This matters enormously for people who need regular medical care.

CSRs are separate from premium subsidies. You can receive both at the same time if you qualify. But you only get CSRs by enrolling in a Silver plan — enrolling in a Bronze plan to get a lower premium means giving up the CSR benefit, which can be a costly trade-off if you use healthcare regularly.

The Individual Mandate: Why It Existed and What Happened to It

When the ACA passed in 2010, it included a requirement that most Americans have health insurance or pay a tax penalty. This was called the individual mandate, or the individual shared responsibility provision. The IRS administered and collected this penalty.

The mandate existed for one specific reason: risk stabilization. Insurance works by spreading risk across a large group of people. Most people in any given year are relatively healthy and pay premiums without making large claims. That money helps cover the costs of the smaller number of people who do get sick. If healthy people can opt out without penalty, they tend to do so — why pay for insurance you don't expect to need? The people who remain insured are, on average, sicker and more expensive to cover. Insurers respond by raising premiums to cover those higher expected costs. Higher premiums push out more healthy people. This cycle is called adverse selection, and at its extreme it's called a death spiral — a market where only sick people are insured and premiums become unaffordable for nearly everyone.

In 2017, Congress reduced the federal penalty to zero, effectively ending the federal mandate starting in 2019. The mandate technically still exists in federal law, but with no penalty, it has no practical force. Several states — Massachusetts, New Jersey, California, the District of Columbia, Rhode Island, and Vermont — responded by creating their own state-level mandates with real penalties. In those states, the mandate still functions as intended. In states without their own mandate, the risk stabilization mechanism it provided is gone.

This matters directly to premiums. Without a mandate, the insured pool in the individual market tilts toward people with higher healthcare needs. Insurers price accordingly. You may not be sicker than you were five years ago — but if the average person in your insurance pool is, your premium reflects that.

Medicaid Expansion: The Gap That Affects Millions

The ACA was originally designed so that everyone up to 138% of the FPL would be covered by Medicaid — the joint federal-state program for people with low incomes — while people above that threshold would qualify for marketplace subsidies. Together, these were supposed to eliminate the gap where someone earns too little to afford marketplace coverage but too much to qualify for traditional Medicaid.

In 2012, the Supreme Court ruled in NFIB v. Sebelius that states could not be required to expand Medicaid. Expansion became optional. States that chose not to expand left a coverage gap: people earning below approximately 138% of the FPL who don't qualify for their state's traditional Medicaid program and, because the ACA assumed they'd be covered by Medicaid, don't qualify for marketplace subsidies either. They earn too little for subsidized marketplace coverage and don't qualify for Medicaid — they fall through the floor of both systems.

As of 2024, a small number of states have still not expanded Medicaid, meaning residents in those states may have no affordable coverage option regardless of how the marketplace subsidies are structured. If you or someone you know may be in this situation, our guide to the Medicaid coverage gap explains what options may still exist.

It's worth being clear: Medicaid and Medicare are separate programs. Medicare is the federal health insurance program for people 65 and older and some people with disabilities. Medicaid is the program for people with low incomes. The ACA's expansion provisions apply to Medicaid only.

The Medical Loss Ratio: A Limit on Insurer Profit

The ACA requires that insurers in the individual and small group market spend at least 80% of the premiums they collect on actual medical care and quality improvement — not administration, not profit. This is called the Medical Loss Ratio, or MLR. If an insurer fails to meet this threshold in a given year, they must issue rebates to policyholders.

The MLR rule limits how much of your premium can be captured as profit. It doesn't, however, control what healthcare actually costs. If medical claims rise — because the insured pool is sicker, because drug prices went up, because hospital prices increased — the insurer can raise premiums to cover those costs and still meet the 80% threshold. The MLR is a ceiling on profit extraction, not a cap on premium growth.

Why Marketplace Premiums Don't Affect Most Americans Directly

When you see news coverage about ACA premiums rising dramatically, it's worth knowing the scope of the market being discussed. The individual marketplace covers a relatively small share of Americans. Most people get coverage through an employer, through Medicare, or through Medicaid. Premium changes on the ACA marketplace don't directly affect people in those programs.

This also means the ACA marketplace is more sensitive to the composition of its enrollee pool than a large employer plan would be. A large employer covering thousands of workers has enormous statistical stability — a few very sick employees don't move the needle much. The individual market is smaller and more volatile. Changes to who participates — through mandate repeal, subsidy changes, or Medicaid expansion decisions — have outsized effects on premiums for the people who remain.

What This Means for You: Putting It Together

If your premium went up or your out-of-pocket costs increased, the most useful questions to ask are: Did my subsidy change? Did my income change in a way that affected my subsidy eligibility? Am I on a Silver plan and taking advantage of cost-sharing reductions if I qualify? Do I live in a state with its own individual mandate that might affect insurer behavior?

Here's a simplified checklist of what to do:

1. Log into your marketplace account and check your current subsidy amount. Compare it to last year's. If it dropped, that's often the entire explanation for a higher bill.
2. Update your income estimate if it has changed. Subsidies are based on projected annual income. Underestimating can lead to repayment at tax time; overestimating means you may be leaving money on the table.
3. If your income is below 250% FPL, make sure you're enrolled in a Silver plan to access cost-sharing reductions. Choosing a Bronze plan to save on the monthly premium may cost you far more when you need care.
4. If your income is below 138% FPL, check whether your state has expanded Medicaid. You may qualify for Medicaid instead of a marketplace plan, often at little or no cost.
5. Use the subsidy calculator at healthcare.gov during open enrollment to see your actual options before assuming you can't afford coverage.

The ACA's mechanisms are interconnected. Subsidies, CSRs, the mandate, and Medicaid expansion were all designed to reinforce each other. When one piece weakens, the others work less effectively. That's not a reason for despair — it's a reason to understand exactly which piece affects your situation, so you can navigate around it as effectively as possible.

Sources: Healthcare.gov — How ACA Plans Work, Healthcare.gov — Premium Tax Credits, CMS — Cost-Sharing Reductions, IRS — Individual Shared Responsibility Provision Overview