ACA Health Insurance Marketplace

The Health Insurance Marketplace (also called the "Exchange") is the system created by the Affordable Care Act (ACA) through which individuals and small businesses can shop for, compare, and purchase private health insurance plans that meet federal standards. Operated either by states (State-Based Exchanges) or by the federal government (HealthCare.gov), the Marketplace is the portal through which roughly 24 million Americans obtained 2025 coverage (a record set with the help of the IRA-enhanced premium tax credits, which expired at year-end 2025), with most receiving premium tax credits and cost-sharing reductions that make coverage affordable.

Current Law (2026)

Legal Authority

• 42 U.S.C. § 18031 — Affordable health insurance exchanges (each state shall establish an Exchange — a governmental or nonprofit entity that makes qualified health plans available to individuals and small employers)
• 42 U.S.C. § 18032 — Consumer choice (Exchanges must present plan options in standardized format; metal tier system; quality ratings)
• 42 U.S.C. § 18041 — State flexibility (states may establish their own Exchanges; the federal government operates an Exchange in states that don't)
• 42 U.S.C. § 18021 — Qualified health plan (defines the standards plans must meet to be sold on the Exchange: licensing, essential health benefits, rate review, quality reporting)
• 42 U.S.C. § 18022 — Essential health benefits (plans must cover 10 categories: ambulatory, emergency, hospitalization, maternity, mental health/substance abuse, prescription drugs, rehabilitative, lab, preventive, and pediatric — including dental and vision)

How It Works

The Marketplace is fundamentally a structured shopping platform for health insurance. Before the ACA, individuals buying their own health insurance (not through an employer) faced a fragmented, confusing market where insurers could deny coverage for pre-existing conditions, charge widely varying rates, and offer plans with significant coverage gaps. The Marketplace addresses this through standardization, transparency, and subsidies.

Plan standardization through the metal tier system makes comparison shopping possible. All Marketplace plans must cover the same 10 categories of essential health benefits, and plans are organized into tiers based on actuarial value — the percentage of average healthcare costs the plan covers. Bronze plans (60% AV) have the lowest premiums but highest out-of-pocket costs; Platinum plans (90% AV) have the highest premiums but lowest cost-sharing. A separate Catastrophic plan is available to people under 30.

The premium tax credit is the financial engine that makes Marketplace coverage affordable. Credits are calculated on a sliding scale based on household income relative to the federal poverty level. The credit is pegged to the cost of the second-lowest-cost Silver plan in the consumer's area (the "benchmark" plan) and reduces the premium the consumer pays. Enhanced credits — eliminating the 400% FPL income cap — were enacted through the Inflation Reduction Act and have dramatically increased enrollment.

State-Based Exchanges (California's Covered California, New York's NY State of Health, etc.) operate their own enrollment platforms, customer service, and outreach programs. States that don't operate their own Exchange use the federal platform (HealthCare.gov), where the federal government provides the technology, call center, and enrollment infrastructure. Some states use a hybrid model.

Open enrollment occurs annually, typically from November 1 through January 15. Outside of open enrollment, consumers can only enroll through special enrollment periods triggered by qualifying life events — losing employer coverage, getting married or divorced, having a baby, moving to a new area, or losing Medicaid eligibility. The Navigator program funds community organizations that provide free, in-person enrollment assistance.

How It Affects You

State Variations

Implementing Regulations

• 45 CFR Part 155 — Health Insurance Exchange standards (establishment, approval, certification of QHPs, enrollment processes, eligibility determinations, SHOP exchanges)

• 45 CFR Part 156 — Health Insurance Issuer Standards under ACA (QHP certification, essential health benefits, risk adjustment, reinsurance, advance payments of premium tax credits)

• 45 CFR Part 147 — Health Insurance Reform Requirements (coverage of essential health benefits, guaranteed availability, guaranteed renewability)

• 45 CFR Part 152 — Pre-Existing Condition Insurance Plan (transition to exchanges)

• 42 CFR Part 435 — Medicaid eligibility (alignment with Exchange open enrollment periods)

• 42 CFR Part 457 — CHIP (alignment with Exchange enrollment, beneficiary data exchange)

• 42 CFR Part 440 — Medicaid services (essential health benefits benchmark)

• 42 CFR Part 422 — Medicare Advantage (access to and exchange of health data)

• 45 CFR Part 158 — Medical Loss Ratio Reporting and Rebate Requirements: implements ACA Section 2718 (PHS Act § 2718), requiring health insurance issuers to annually report how they spend premium dollars and to rebate enrollees if they spend too little on medical care. Key provisions:

  • §§ 158.101–158.102 — Applicability: covers all individual and group market health insurance issuers (including grandfathered plans); self-insured employer plans are exempt — the MLR requirement is an issuer obligation, not an employer benefit obligation
  • § 158.110 — Annual MLR report to HHS Secretary: issuers must file detailed financial data within 6 months after the end of each calendar year, broken down by state and market (individual, small group, large group)
  • § 158.130 — Premium revenue calculation: the denominator; includes earned premiums less taxes and licensing fees; excludes risk corridor payments and reinsurance — the calculation isolates the pure insurance premium that should translate into medical value
  • § 158.140 — Medical claims reimbursement: the primary numerator component; counts actual incurred claims paid, including amounts paid to hospitals, physicians, and other providers
  • § 158.150 — Quality improvement activities (QIA): counts toward MLR as medical spending; includes programs to improve patient safety, reduce hospital readmissions, implement evidence-based medicine, and enhance care coordination — allowing insurers to count health management programs (disease management, care management) as "medical" spending
  • § 158.210 — Minimum MLR thresholds: large group market — 85% of premium revenue must go to medical claims and QIA; individual and small group markets — 80%. Issuers that fall short must rebate the shortfall to enrollees — in the form of premium credits, lump-sum checks, or premium reductions — by September 30 following the reporting year

  The MLR rule is one of the ACA's most concrete consumer-protection mechanisms: it caps insurer administrative costs and profit at 15-20% of premium and creates an automatic rebate if the cap is breached. Approximately $3–9 billion in MLR rebates have been paid in various years since the requirement took effect in 2011. Individual market rebates go directly to policyholders; group market rebates go to employers, who must pass them through to employees in proportion to each employee's premium contribution. The MLR calculation has been litigated over which activities count as QIA vs. administration — particularly for wellness programs and care management vendors.

• 45 CFR Part 150 — CMS Enforcement of Individual and Group Market Requirements: establishes how the federal government enforces the ACA's health insurance market reforms when states fail to do so. Key provisions:

  • § 150.101 — Statutory authority: CMS enforces health insurance market requirements under PHS Act §§ 2723 (group and individual markets) and 2761 (ERISA plans with state law exclusions); the enforcement authority is concurrent — states go first, CMS steps in only when state enforcement breaks down
  • § 150.201 — Primary state enforcement: states are the default enforcers of PHS Act market requirements applicable to health insurance issuers operating within their borders; CMS does not routinely enforce in states with adequate enforcement programs
  • § 150.203 — When CMS assumes enforcement authority: CMS enforcement is triggered in three circumstances — (1) a state notifies CMS that it does not have authority or the means to enforce a specific requirement; (2) the state waives enforcement; or (3) CMS determines after notice and opportunity to respond that the state has failed to substantially enforce a requirement. Each trigger is issuer-specific and requirement-specific — CMS can assume enforcement of one provision (e.g., mental health parity) while the state continues enforcing others
  • Subpart B (11 sections, §§ 150.201–150.225) — Procedures for making state enforcement failure determinations: CMS must notify the state of potential failures, provide a 30-day response period (extendable for good cause), consider state explanations, and document findings before assuming enforcement — an administrative due process structure designed to make federal takeover a last resort, not a routine oversight mechanism
  • Subpart C (17 sections, §§ 150.301–150.345) — Civil money penalties: CMS may impose civil money penalties on issuers that violate ACA market requirements after CMS has assumed enforcement; penalties accrue per day of violation and per enrollee or policy affected; maximum penalties align with HIPAA/PHS Act ceilings; issuers may request a reduction or waiver based on financial hardship or corrective action already taken
  • Subpart D (32 sections, §§ 150.401–150.475) — Administrative hearing procedures: the largest subpart; establishes the procedural rights of issuers facing civil money penalties — notice of proposed penalty, right to hearing before an ALJ, briefing and evidence rules, ALJ decision, appeal to the DAB (Departmental Appeals Board), and judicial review; the elaborate hearing process reflects the constitutional due process requirements for government-imposed penalties

  Part 150's backstop structure reflects a deliberate policy judgment embedded in the ACA: insurance market regulation is primarily a state function, but the federal government must have the ability to enforce core protections when states cannot or will not. The result is a two-tier enforcement system — the typical consumer experience of insurance market rules involves state insurance commissioners, not CMS, because most states do actively enforce. CMS Part 150 enforcement has been used most often in cases involving mental health parity (MHPAEA) violations and surprise billing requirements where specific issuers fell outside state jurisdiction.

• 42 CFR Part 600 — Basic Health Program (BHP) (49 sections across 8 subparts — implements ACA Section 1331, which gives states the option to create a Basic Health Program as an alternative to the standard Marketplace for residents at 133–200% of the federal poverty level; as of 2026, only New York (Essential Plan) and Minnesota (MinnesotaCare) operate BHPs):

  • § 600.1 — Scope: a BHP is a state-administered program under which the state contracts with standard health plans to provide coverage to eligible individuals; the state receives federal funding equal to 95% of what the federal government would have spent on advance premium tax credits (APTCs) and cost-sharing reductions (CSRs) if those individuals had enrolled in Marketplace plans — making BHP financially attractive to states with large low-income populations near the Medicaid/Marketplace boundary
  • § 600.110 — BHP Blueprint: a state seeking to establish a BHP must submit a comprehensive "Blueprint" to HHS describing the program design, eligibility criteria, benefits package, standard health plan requirements, payment structures, and administrative arrangements; HHS certifies the Blueprint before the program may operate
  • § 600.120 — Blueprint certification: HHS must act on Blueprint submissions in a timely manner; interim certification is available while final review proceeds; states may not enroll individuals until HHS certifies the Blueprint; revisions require re-submission and approval (§ 600.125)
  • § 600.200 — Eligibility (Subpart D): individuals are eligible for BHP if they are (1) residents of the state, (2) not eligible for Medicaid, CHIP, or affordable employer-sponsored insurance, (3) between 133% and 200% FPL, and (4) lawfully present non-citizen immigrants ineligible for Medicaid due to immigration status; states may extend coverage to lawfully present immigrants at 0–133% FPL who are ineligible for Medicaid — a significant option that New York used to cover undocumented immigrants through state funding supplements
  • Subpart E — Standard Health Plans: the coverage provided through BHP must meet or exceed the essential health benefit requirements that apply to Marketplace QHPs; standard health plans must offer the same services as a Marketplace silver plan; premium contributions and cost-sharing are generally lower than Marketplace silver plans, reflecting the BHP's target population at incomes where out-of-pocket costs are a significant access barrier
  • Subpart F — Enrollee Financial Responsibilities: BHP states set premiums and cost-sharing within federal limits; the federal government's 95% funding contribution is designed to allow states to offer premiums below what Marketplace plans would cost; New York's Essential Plan charged $0 premiums until a 2023 expansion
  • § 600.605 — BHP Trust Fund (Subpart H): federal BHP payments are deposited into a state-held trust fund; the state may only use trust fund monies for BHP program costs; unused trust fund amounts revert to the federal government; the trust fund structure enforces additionality — states cannot divert BHP federal payments to general state purposes

  The BHP is the ACA's least-used coverage option, primarily because it requires states to establish administrative infrastructure and take on program management responsibilities. The federal funding formula (95% of the APTC/CSR that would have been paid) creates a strong fiscal incentive: states receive near-full federal reimbursement while keeping enrollees in a state-designed program rather than the federal Marketplace. New York's Essential Plan enrolled over 1.3 million people as of 2025, making it the largest public health insurance program in New York state after Medicaid. The 2024 CMS rule (89 FR 22878) clarified BHP funding calculations for states expanding coverage to income bands below 100% FPL.

  Recent rulemakings: 89 FR 22878 (April 2024) — updated BHP payment methodology for state coverage expansions to 0–100% FPL immigrants; 88 FR 79555 (November 2023) — technical corrections and clarifications to BHP Blueprint and eligibility rules.

• 45 CFR Part 154 — Health Insurance Issuer Rate Increases: Disclosure and Review Requirements: implements ACA Section 2794 (PHS Act), establishing a federal rate review process for large premium increases by individual and small group market health insurance issuers. Key provisions:

  • § 154.200 — Rate increases subject to review: a rate increase is subject to federal review if it is 10% or more (or a lower threshold set by the state); the 10% threshold applies on a product-by-product basis; issuers filing rate increases below the threshold are not subject to the disclosure and review requirements of this Part, though state law may impose additional review
  • § 154.205 — Unreasonable rate increases: CMS will determine a rate increase to be "unreasonable" if it is excessive (not justified by actual costs), unjustified (not actuarially supported by trend data and claims experience), or unfairly discriminatory among similarly situated enrollees; a finding of "unreasonable" does not legally block the rate increase in most states — the federal review is advisory unless the state has CMS-certified "effective rate review" authority
  • § 154.210 — Review by CMS or state: if a state has an "Effective Rate Review Program" (certified by CMS under § 154.301), the state conducts the review; otherwise CMS reviews the filing directly; most states have effective rate review programs, making CMS the fallback reviewer rather than the primary reviewer
  • § 154.215 — Rate Filing Justification: issuers must submit a detailed rate filing justification to CMS and the applicable state before implementing a rate increase subject to review; the justification includes the proposed rate change, the actuarial memorandum supporting the change, the medical trend components, and the historical loss ratio data; the justification must be submitted at least 60 days before the proposed effective date (or earlier if the state requires)
  • § 154.225 — CMS or state determination: after reviewing the rate filing justification, CMS or the state issues a preliminary finding of "reasonable" or "unreasonable"; the issuer may respond to a preliminary finding of unreasonable before a final determination is made
  • § 154.230 — Public posting of final justifications: if a rate increase is ultimately found unreasonable but the issuer implements it anyway (which is legally permissible in many states), the issuer must publicly post a final justification on its website explaining why it chose to implement an unreasonable rate increase; CMS also posts determinations on its website at ratereview.healthcare.gov, creating a public record of rate review outcomes by state and issuer
  • § 154.301 — Effective Rate Review Programs: CMS evaluates state rate review programs and certifies those that meet federal standards; a state with an Effective Rate Review Program conducts binding review (the state can block or require modifications to unreasonable rate increases); states without effective programs have advisory review only; as of 2026, the majority of states have effective programs, with significant variation in how aggressively they exercise review authority

  The rate review framework is one of the ACA's tools for consumer protection in the insurance market, but its practical impact is limited by the advisory nature of federal review: CMS can label a rate increase "unreasonable" but cannot block it without state legal authority. States with robust rate review programs (Massachusetts, New York, California) can and do require modifications; states without statutory authority to reject rates can only publish unfavorable findings. The public posting requirement at ratereview.healthcare.gov has created transparency around large rate filings — consumer advocates and journalists regularly review the database when major rate increases are filed. Recent rulemaking: 83 FR 17060 (April 2018) adjusted the minimum threshold and review procedures; 80 FR 10864 (February 2015) updated rate review rules for market stability.

• 45 CFR Part 153 — Standards Related to Reinsurance, Risk Corridors, and HHS Risk Adjustment: implements the ACA's "Three Rs" — three interlocking programs designed to stabilize insurance markets during and after the ACA's initial years. Each program addresses a different type of risk:

  Transitional Reinsurance (2014–2016, Subpart C): the ACA required all health insurers (including self-insured employer plans) to contribute to a transitional reinsurance pool; HHS used the collections to reimburse individual market insurers who enrolled high-cost individuals above an attachment point threshold; in 2014, the attachment point was $45,000 (costs above this amount were reimbursed at 80% up to a $250,000 cap); the program was temporary — scheduled to wind down after 2016 when the risk adjustment program was expected to be sufficient; reinsurance distributions reduced individual market premiums by an estimated 10–14% during the transition period; the funding mechanism (per-enrollee assessment on all health plans, including employer plans) generated political controversy because employer plans paid into a pool that only benefited individual market insurers.

  • § 153.210 — State establishment of reinsurance programs: states could establish their own reinsurance programs using the federal reinsurance funds; states that did so received the national reinsurance funds and applied them under their own parameters (different attachment points, reinsurance rates); HHS established a default federal program for states that did not operate their own; as of 2024, a growing number of states have established permanent state-based reinsurance programs (known as "1332 waivers") that continue after the federal program expired
  • § 153.220–153.230 — Contributions and payment calculations: all contributing entities paid a per-covered-life assessment; the contribution rate was set nationally each year; HHS collected contributions and calculated reinsurance payments based on actual high-cost claims across the national pool

  Risk Corridors (2014–2016, Subparts E–G): a temporary program that shared gains and losses between insurers and the federal government; insurers whose costs were lower than predicted (windfall profits) paid a portion to the government; insurers whose costs were higher than predicted (losses) received payments from the government; the risk corridor program was designed to protect insurers from mispricing risk in the new ACA markets during the first three years. A congressional appropriations rider in 2014 limited risk corridor payments to what was collected (not allowing HHS to use other funds if collections were insufficient); because enrollment skewed sicker than expected, collections were far below payments owed — insurers received only a fraction of the risk corridor payments they were entitled to. The Supreme Court ultimately ruled (Maine Community Health Options v. U.S., 2020) that the government owed insurers the full unpaid risk corridor amounts, resulting in a multi-billion-dollar federal liability paid to carriers.

  Permanent Risk Adjustment (Subpart D): unlike the two temporary programs, risk adjustment is a permanent, budget-neutral program that continues indefinitely; it redistributes money among individual and small group market insurers within each state based on the relative risk of their enrolled populations; insurers with healthier-than-average enrollees pay into the risk adjustment pool; insurers with sicker-than-average enrollees receive payments from the pool; the net amount transferred is zero — it's a redistribution, not a subsidy.

  • § 153.320 — HHS risk adjustment methodology: HHS calculates each insurer's "plan liability risk score" based on the health status and demographic characteristics of its enrollees; the risk scores are calculated from diagnoses in claims data submitted by issuers; HHS uses its own risk adjustment model (not commercial models) — the coefficients are recalibrated annually; an insurer whose enrollees have higher-than-average predicted costs receives risk adjustment payments; an insurer whose enrollees have lower-than-average predicted costs makes payments
  • § 153.340 — State risk adjustment programs: states may operate their own risk adjustment programs using alternative methodologies if HHS certifies that the state methodology is actuarially sound; Massachusetts, for example, had an existing risk adjustment program before the ACA; most states use the HHS-operated federal program by default
  • § 153.350 — HHS-operated risk adjustment: for states that do not operate their own program, HHS both calculates the risk adjustment transfers and collects/disburses the funds; HHS charges an administrative fee (0.2% of premium) to cover program costs; the risk adjustment program has transferred hundreds of billions of dollars cumulatively since 2014, reducing the incentive for insurers to cherry-pick healthy enrollees

  Significance: Risk adjustment is the foundational market stabilization mechanism for the ACA individual market. Without it, insurers would have strong financial incentives to design benefits and market plans to attract healthy enrollees and avoid sick ones — "risk selection" that would ultimately cause the insurance market to collapse (adverse selection death spiral). By redistributing money from insurers with healthy enrollees to insurers with sick ones, risk adjustment makes it financially neutral (in theory) to serve any risk pool. Recent rulemakings: 77 FR 17248 (March 23, 2012) — initial rule establishing the Three Rs framework; 78 FR 65094 (October 30, 2013) — amendments to risk adjustment methodology. Annual updates to the HHS Notice of Benefit and Payment Parameters (published each winter) recalibrate risk adjustment coefficients for each coming plan year.

Pending Legislation

• S 3380 — Require $5 minimum monthly premium for tax credit recipients, photo ID checks for Marketplace enrollees. Status: Introduced.
• HR 7861 — Raise MLR floor to 85% for small/individual plans, add penalties for false ACA Exchange enrollments. Status: Introduced.
• SJRES 84 (Sen. Kaine, D-VA) — Block CMS rule on ACA marketplace integrity and affordability via CRA. Status: In committee.

Recent Developments

• Record enrollment of 24+ million (2025): driven by IRA subsidies, not the mandate: Open enrollment for plan year 2025 set another record — approximately 24.2 million people selected Marketplace plans (CMS final report). The driving force was the Inflation Reduction Act's enhanced premium tax credits, which eliminated the 400% FPL income ceiling and capped premiums at 8.5% of income. The individual mandate penalty has been $0 since 2019 — the enrollment surge proves the mandate was never the key to ACA's viability.
• IRA enhanced credits expired Dec 31, 2025: The Senate failed to advance an extension in December 2025 (the Lower Health Care Costs Act, S. 3385, did not clear cloture), and the enhanced credits expired on January 1, 2026. Premium tax credits reverted to the pre-2021 schedule (capped at 400% FPL with no 8.5% premium ceiling). Plan-year 2026 open enrollment numbers ran behind plan-year 2025 as a result; KFF estimates average premium payments roughly doubled for many subsidized enrollees absent extension. As of May 2026, a bipartisan Senate group is negotiating a two-year reinstatement (the proposed CARE Act), but no extension has been enacted.
• Trump administration's CMS marketplace integrity actions (2025–2026): The Biden-era CMS rule on ACA marketplace integrity and affordability — which streamlined continuous enrollment and reduced documentation requirements — faced a Congressional Review Act challenge (SJRES 84). CMS under the Trump administration also increased scrutiny of broker-driven enrollments, particularly after investigations revealed some Enhanced Direct Enrollment brokers had enrolled people in plans without their knowledge to collect commissions. CMS implemented new verification requirements affecting agent-assisted enrollments.
• "Great Healthcare Plan" White House initiative (January 2026): President Trump launched a White House initiative presenting the administration's healthcare vision, including expanded health savings accounts, price transparency requirements, and promotion of short-term health plans as ACA alternatives. The proposal did not include legislation to repeal or replace the ACA exchanges but signaled continued executive interest in expanding alternative coverage models. Short-term health plans — which don't cover essential health benefits and can exclude pre-existing conditions — remain the primary alternative for unsubsidized buyers priced out of the Marketplace.