Under the Affordable Care Act, health insurers selling individual and small-group plans must use guaranteed issue: they must sell every plan to every applicant who applies during open enrollment or a special enrollment period, regardless of health history, and they cannot price the premium on your medical conditions or claims. Rating factors are limited by statute to five: age (with a three-to-one cap between the oldest and youngest adults), geography (by rating area), tobacco use (a 50 percent maximum surcharge), family size, and the metal tier of the plan. Before 2014, individual underwriting routinely meant denial for diabetes, cancer history or even prior cesarean delivery; the statutory change eliminated that practice for ACA-compliant coverage — a shift documented in CMS marketplace regulations.
This site publishes information, not medical or insurance advice. The rules described here govern ACA-compliant plans; short-term policies, certain employer arrangements and most non-health insurance products still use conventional underwriting, and state variations are real. Confirm specifics for any product before you buy.
How the five rating factors actually move your premium
Age produces the widest swing. A 64-year-old's base rate may be three times a 21-year-old's, before any subsidies. Geography matters more than people expect: moving between counties within one state can change premiums substantially because rating areas reflect local provider prices, and a cross-country move is a special enrollment event precisely because prices differ. Tobacco surcharges reach 50 percent of the base rate — the single largest lawful health-related penalty in ACA pricing, though some states have capped or eliminated them. Family size rates children at a flat per-child factor up to three children. Metal tier sets the price-quality tradeoff but not a penalty: a Bronze and a Platinum for the same person differ by plan richness, not by risk.
Subsidies interact with these rating factors in ways that flatten the effective curve. Because premium tax credits cap what households pay as a share of income, the age-based spread in net cost shrinks dramatically for subsidized enrollees — a 62-year-old paying triple the 27-year-old's gross premium may pay nearly the same net after the credit, which is why gross premiums alone mislead older shoppers comparing plans. Conversely, tobacco users owe the surcharge even after subsidies in most cases, since the credit does not absorb it, and some carriers verify tobacco use through attestations checked at audit rather than testing.
What insurers adjusted to stay profitable under those rules
With medical underwriting off the table, plans influence their risk pool through design rather than selection. Narrow networks steer certain conditions; drug formulary placement and prior authorization shape utilization; and metal-tier pricing remains a lawful lever — a plan priced to attract healthy enrollees will look cheap until claims experience forces a correction. The clearest evidence of residual selection pressure is the long-running debate over cost-sharing reduction payments and silver loading, where pricing decisions in one plan category visibly shifted prices in others. Guaranteed issue changed who must be offered coverage; it did not end the economics of adverse selection, only relocated them.
Related stories: HSA vs FSA: Which Health Spending Account Fits Your Budget and Tax Situation · Claim Denied? How the Internal and External Appeal Process Actually Works.
Where old-style underwriting still lives
- Short-term limited-duration plans: under federal rules finalized in 2024, these remain medically underwritten in most states, can deny applicants and exclude pre-existing conditions; their duration limits were tightened back to about three to four months with limited renewal.
- Large-group employer plans: guaranteed issue applies to employees, but employers manage risk through plan design and wellness programs whose financial incentives are capped by regulation.
- Life, disability and long-term care insurance: fully underwritten on health, family history, and in the case of life insurance, often biomarkers and prescriptions reviewed from records you authorize.
- Health care sharing ministries: not insurance, no guaranteed acceptance, and no regulatory obligation to pay a claim.
Group rating caps tell a similar story on the small-employer side. Carriers may look through a firm's census and price the whole group on the age-geography-tobacco formula, but they cannot deny the group or surcharge it because one employee has expensive claims. That is the quiet achievement of guaranteed issue for small businesses: before 2014, a single employee's cancer diagnosis at renewal could reprice an entire firm's coverage or push the carrier to decline renewal outright. Renewal increases today flow through claims experience of the whole market and regulated rate review, a process state insurance departments publish, including the medical-loss-ratio floors that require at least 80 to 85 cents of each premium dollar to fund care or be rebated.
Special enrollment periods are the loophole that matters
Because guaranteed issue is time-gated, losing other coverage, marriage, birth, or a permanent move opens a 60-day special enrollment window on the marketplace — and unlike the pre-ACA world, entering mid-year with a serious diagnosis cannot be refused or surcharged. For anyone leaving employer coverage, the sequence matters: COBRA election rights, marketplace eligibility, and the special enrollment clock interact, and electing COBRA before checking marketplace subsidies can forfeit options for the rest of the year.
What to do before you sign anything
Ask one question of any health plan that is not through the marketplace, your employer, Medicare or Medicaid: is this ACA-compliant coverage with guaranteed issue, or medically underwritten? The answer changes every other term of the deal — pre-existing condition exclusions, annual caps, and the enforceability of the promised benefits. If the product turns out to be short-term or a sharing arrangement, treat its documents the way an underwriter would: read the exclusions first, not the price.
For more context, read Medicare Advantage vs Medigap: The Two Roads After Original Medicare.
For more context, read employer open enrollment.
For more context, read medicaid expansion eligibility.