Health insurance is a contract that splits the cost of your medical care with an insurer according to fixed rules. You pay a monthly premium to keep the plan active, then share the cost of care through a deductible and either copays or coinsurance until you hit an annual ceiling; after that, the insurer pays 100% of covered services for the rest of the plan year. Understanding how health insurance works comes down to four moving parts: what you pay, what the plan covers, when you can enroll, and what happens when a claim is filed or denied. For 2026, federal law caps your maximum out-of-pocket spending at $10,600 for an individual plan and $21,200 for a family plan, so there is a hard limit on how much any covered year can cost you.
What You Pay and When
Costs fall into two buckets: what you pay to have coverage, and what you pay when you use it.
Your premium is the recurring payment, usually monthly, that keeps the plan active. In the individual and small-group markets, insurers can only use four factors to set your rate: your age (older adults pay no more than three times what younger adults pay), tobacco use (up to 1.5 times the non-tobacco rate), your geographic rating area, and whether the plan covers just you or your family. Health history and gender cannot affect the price.
Your deductible is what you pay out of pocket before the plan starts sharing costs. On a plan with a $2,000 deductible, the first $2,000 of covered services comes from you. After that, you split costs with the insurer through copays (a flat fee per service, such as $30 for a specialist visit) or coinsurance (a percentage of the bill, such as 20% of a hospital stay).
Cost-sharing continues until you reach the plan’s annual out-of-pocket maximum. For 2026, federal rules cap that at $10,600 for individual coverage and $21,200 for family coverage. Once you hit the ceiling, the insurer pays 100% of covered in-network services for the rest of the plan year. Preventive care that is covered at no cost does not count toward your deductible or maximum, because you never paid anything toward it in the first place.
What Your Plan Has to Cover
Every plan must give you a Summary of Benefits and Coverage, a standardized plain-language document that lays out what is covered, what it costs, and what is excluded. Insurers and employers provide it free of charge before you enroll, and it is the cleanest way to compare plans side by side.
Under the Affordable Care Act, non-grandfathered plans in the individual and small-group markets must cover ten categories of essential health benefits:
- Outpatient care
- Emergency services
- Hospitalization, including surgery
- Maternity and newborn care
- Mental health and substance use treatment
- Prescription drugs
- Rehabilitative services and devices
- Lab services
- Preventive and wellness services
- Pediatric services, including dental and vision for children
Plans cannot deny you coverage or charge more because of a preexisting condition, and once you are enrolled the insurer cannot drop you based on your health. Federal law requires renewal as long as you keep paying premiums; the only grounds for nonrenewal are nonpayment, fraud, breaking participation rules, the insurer leaving the market, or no enrollees remaining in the service area.
Certain preventive services must be covered with no copay, coinsurance, or deductible when you use an in-network provider. That includes recommended immunizations, cancer screenings, blood pressure and cholesterol checks, and well-child visits.
When You Can Enroll
You cannot buy most health coverage whenever you want. Missing the window can leave you uninsured for months.
Marketplace and Employer Plans
ACA marketplace open enrollment typically runs from November 1 through January 15, with coverage starting as soon as January 1 if you sign up early enough. Employer plans hold their own open enrollment, usually once a year in the fall. Outside those windows, you can enroll or change plans only after a qualifying life event: marriage, a new baby, losing other coverage, or moving to a new area, among others. You generally have 60 days from the event to act.
Employers can impose a waiting period on new hires, but federal law caps it at 90 days.
Medicare
Your initial Medicare enrollment period runs for seven months: three months before the month you turn 65, the birthday month itself, and the three months after. Miss it, and you can sign up during the general enrollment period from January 1 through March 31, but coverage will not start until July. You will also owe a Part B late enrollment penalty: 10% added to your monthly premium for every full 12-month period you could have been enrolled and were not. That surcharge stays with you as long as you have Part B, which for most people is permanent.
Medicaid and CHIP
Medicaid and the Children’s Health Insurance Program do not follow open enrollment. You can apply year-round if you meet income and household rules. Eligibility is based on modified adjusted gross income. Since January 2024, children under 19 enrolled in Medicaid or CHIP get 12 months of continuous coverage regardless of income changes during that period.
Using the Plan: Claims and Networks
A claim is the formal request for payment your provider sends the insurer after you receive care. In most cases the provider files it electronically. Claims usually have a filing deadline set by the plan, often somewhere between 90 days and a year from the date of service.
The insurer reviews each claim against your plan’s terms. Is the service covered? Was it medically necessary? Did it need preauthorization? Was the provider in network? A claim that fails any of those checks can be denied or reduced. Out-of-network care is generally reimbursed at a lower rate, leaving you responsible for the difference between the provider’s charge and what your plan pays.
If you are covered by two plans, coordination of benefits rules decide which pays first. Usually the plan where you are the primary policyholder pays first and the plan where you are a dependent pays second. For children covered by both parents, the birthday rule generally applies: the parent whose birthday falls earlier in the calendar year holds the primary plan. Combined payments will not exceed the total cost of care, but two plans can meaningfully reduce what you owe.
Protection From Surprise Medical Bills
The No Surprises Act, in effect since January 2022, shields you from unexpected bills in situations you cannot control. For emergency care, you pay only your in-network cost-sharing regardless of whether the hospital or treating doctors are in your plan’s network. The same rule applies when you receive care at an in-network facility but are treated by an out-of-network provider you did not choose, such as an anesthesiologist or radiologist. Those amounts count toward your in-network deductible and out-of-pocket maximum.
If you are uninsured or paying out of pocket, providers must give you a good faith estimate of expected charges before scheduled care. If the final bill exceeds that estimate by $400 or more, you can dispute it through a federal process. When an insurer and an out-of-network provider cannot agree on payment, either side can trigger independent dispute resolution: each submits a proposed amount, a neutral arbitrator picks one, and the losing side pays within 30 days.
What to Do if a Claim Is Denied
A denial is not the end. Federal law gives you the right to challenge it, and the insurer must explain the reason in writing, citing the specific policy provision or medical necessity standard it applied.
Internal Appeal
The first step is an internal appeal with the insurer. Federal timelines depend on the situation:
- Urgent care denials: the insurer must decide within 72 hours
- Pre-service denials, for care you have not received yet: 30 days
- Post-service denials, for care already received: 60 days
Many denials come from fixable problems: a missing preauthorization, incorrect procedure codes, or incomplete documentation. A letter from your doctor explaining why the treatment was necessary can flip the outcome. This is where most disputes are actually won or lost.
External Review
If the internal appeal fails, you can request an external review by an independent review organization that has no financial relationship with your insurer. You have four months from the internal denial to file. The reviewer looks at your medical records, your doctor’s reasoning, and relevant clinical guidelines, then issues a binding decision. Standard cases must be decided within 45 days; urgent cases within 72 hours. If the reviewer overturns the denial, the insurer must provide coverage or payment immediately.
Many states also run consumer assistance programs staffed by health insurance ombudsmen who can help you file appeals and complaints at no charge. If you believe your insurer is acting in bad faith, you can file a complaint with your state insurance department, which can investigate, fine, or order corrective action.
Keeping Coverage After You Lose a Job
If you lose employer-sponsored coverage, COBRA may let you keep the group plan temporarily. It applies to employers with 20 or more employees. Different qualifying events trigger different durations:
- Job loss or reduced hours: 18 months for the employee and covered dependents
- Divorce or legal separation: 36 months for the former spouse and dependents
- Death of the covered employee: 36 months for the surviving spouse and dependents
- A child aging out of dependent status: 36 months
The cost is the catch. While you were employed your employer likely paid a large share. Under COBRA you pay up to 102% of the full premium (both portions plus a 2% administrative fee); for the disability extension covering months 19 through 29, the plan can charge up to 150%. You have 60 days from the date of your COBRA notice to elect coverage, and it applies retroactively to the date you lost the employer plan.
HSAs and High-Deductible Plans
A health savings account lets you set aside pre-tax money for medical expenses, but only if you are enrolled in a qualifying high-deductible health plan. For 2026, an HDHP must carry a minimum annual deductible of $1,700 for self-only coverage or $3,400 for family coverage, and total out-of-pocket costs cannot exceed $8,500 self-only or $17,000 family.
The 2026 HSA contribution limits are $4,400 for individuals and $8,750 for families. Contributions reduce your taxable income, the balance grows tax-free, and withdrawals for qualified medical expenses are tax-free as well. You cannot contribute if you are enrolled in Medicare or claimed as a dependent on someone else’s return. If you are 55 or older, you can add another $1,000 per year as a catch-up contribution.
If You Get a Marketplace Subsidy, Reconcile at Tax Time
If you buy coverage through the ACA marketplace, you may qualify for advance premium tax credits that lower your monthly premium based on estimated household income. Because the advance is built on an estimate, the IRS requires a true-up when you file. You use Form 1095-A from the marketplace and Form 8962 on your return. If your actual income came in lower than estimated, you get more credit; if it came in higher, you owe some or all of the advance back.
For plan year 2026, there is no cap on the amount of excess advance credits you have to repay, at any income level. In prior years, repayment was limited for households below 400% of the federal poverty line, but that protection no longer applies. Failing to reconcile by filing Form 8962 disqualifies you from receiving advance credits or cost-sharing reductions the following year. Updating your marketplace application whenever your income changes, from a raise, a new job, or a spouse starting work, is the practical way to avoid a large bill in April.