An ACO health plan is a healthcare arrangement where a group of doctors, hospitals, and other providers agree to work together as a team to coordinate your care and keep costs down. ACO stands for Accountable Care Organization, and it’s most commonly associated with Medicare, though private insurers have adopted similar models. The core idea: instead of each provider operating independently and billing separately for every service, they share responsibility for your overall health and are financially rewarded when they keep you healthy and avoid unnecessary spending.
How an ACO Works
In a traditional fee-for-service system, every office visit, lab test, and procedure generates a separate bill. Providers have no financial reason to coordinate with each other, and no one is penalized when a patient falls through the cracks between specialists, hospitals, and primary care. An ACO flips that model. A defined group of providers collectively takes responsibility for a specific population of patients, and they’re measured on both quality of care and total cost.
If the ACO delivers high-quality care while spending less than a projected benchmark, the providers share in those savings. If care is fragmented and costs go up, the ACO may owe money back. This creates a direct incentive for your doctors to talk to each other, avoid duplicate tests, prevent unnecessary hospital readmissions, and focus on keeping you healthy rather than just treating problems after they arise.
The Financial Model Behind ACOs
ACOs operate under one of two financial arrangements. In a one-sided risk model, the ACO can earn bonus payments when it saves money, but doesn’t owe anything if costs exceed the benchmark. This is the lower-risk entry point that lets provider groups test the model. In a two-sided risk model, the ACO shares in savings when it performs well but also pays a penalty when spending rises above the target. The potential rewards are larger, but so is the financial exposure.
Some ACOs go even further. Under the ACO REACH Model, providers can choose a “professional” track with 50% shared savings and losses, or a “global” track where they accept 100% of savings and losses. In the global option, the ACO receives a risk-adjusted monthly payment covering all covered services, essentially taking on full financial responsibility for patient care. These higher-stakes arrangements push providers to invest more heavily in prevention and coordination because wasted spending comes directly out of their shared budget.
What This Looks Like for Patients
If you’re in Medicare and your primary care provider participates in an ACO, you’re typically “assigned” to that ACO based on where you receive most of your primary care. In traditional Medicare ACOs, you aren’t locked into a network. You retain the right to see any Medicare-accepting provider. The ACO simply tracks and coordinates your care behind the scenes. This is a key difference from an HMO, where going out of network usually means paying the full cost yourself.
What you’re more likely to notice is better follow-up. ACOs embed care managers in emergency departments who alert your primary care doctor when you visit the ER. After a hospital stay, many ACOs send someone to your home within three to five days to review your discharge instructions, reconcile your medications, and check that your living situation supports recovery. If you have a chronic condition like diabetes or heart failure, you may get regular coaching on self-management, team-based medication reviews involving pharmacists, and closer monitoring between visits. The goal is to catch problems early and prevent the kind of crises that lead to expensive hospitalizations.
How Quality Is Measured
ACOs don’t just save money to earn rewards. They also have to meet quality standards across several categories. CMS evaluates ACOs on 33 quality measures spanning patient experience, care coordination, preventive health, and management of chronic conditions.
On the patient experience side, ACOs are scored on how easily you can get timely appointments, how well your doctors communicate, and whether you’re involved in shared decision-making about your treatment. For care coordination, measures include hospital readmission rates, medication reconciliation after discharge, and whether providers use electronic health records to share information. Preventive health metrics track cancer screenings, flu vaccinations, blood pressure checks, tobacco use counseling, and depression screening.
For patients with chronic conditions, the measures get more specific. ACOs are evaluated on how well they manage blood sugar levels in people with diabetes, blood pressure control in people with hypertension, and appropriate medication use for patients with heart disease. An ACO that cuts costs by skimping on necessary care would fail these quality benchmarks and lose its shared savings payments.
Are ACOs Actually Saving Money?
The most recent data suggests they are, and the trend is accelerating. In 2024, ACOs in Medicare’s Shared Savings Program achieved the highest savings rates since the program launched. Out of 476 participating ACOs, 75% earned performance payments, covering about 80% of the 10.3 million patients assigned to the program. Those ACOs generated $4.1 billion in shared performance payments, while Medicare itself saved $2.5 billion relative to spending benchmarks.
Per-person savings also grew. Net savings per patient (the portion Medicare keeps) rose from $207 in 2023 to $245 in 2024. Gross savings per patient, split between ACOs and Medicare, jumped from $515 to $651 over the same period. These aren’t abstract accounting figures. They reflect fewer unnecessary hospital stays, better chronic disease management, and more efficient use of healthcare resources across millions of patients.
ACOs vs. Other Health Plan Models
ACOs are sometimes confused with HMOs or PPOs, but they work differently. An HMO requires you to choose providers within a defined network and typically requires referrals to see specialists. A PPO gives you more flexibility but charges higher costs for out-of-network care. An ACO in traditional Medicare doesn’t restrict your provider choices at all. It’s a coordination layer on top of your existing coverage, not a replacement for it.
Private insurers have also built ACO-style arrangements, sometimes marketed as “ACO health plans” or “accountable care plans.” These commercial versions may function more like a traditional insurance plan with a defined network, so the rules around provider choice can vary. If you’re considering a commercial ACO plan, it’s worth checking whether it limits your providers the way a Medicare ACO does not.
The defining feature of any ACO, whether Medicare or commercial, is the accountability structure. Your providers have a financial stake in your outcomes. That creates a fundamentally different dynamic than a system where every appointment and test is just another billing event.