Health care accounts for nearly one-fifth of the US economy, and national health expenditures are projected to exceed 20% of gross domestic product by 2033.1 After decades of concern about rising expenditures, growing evidence suggests that the US has experienced a sustained slowdown in health spending growth relative to historical trends and earlier projections.2 Whether the US has successfully “bent the cost curve” has become a prominent focus of health policy debate.

Yet spending growth is only one dimension of sustainability and should be considered alongside spending levels and the distribution of financial burden. During the period in which the US bent the cost curve, the disconnect between health care spending, affordability, and population health outcomes has become increasingly pronounced.3,4 For a country that already devotes far more resources to health care than any other,5 even modest growth may have important implications for affordability and access while raising persistent questions about whether spending levels generate sufficient value.

Given the already high level of US health care spending and growing concerns about affordability, policymakers face a fundamental challenge: improving affordability often requires investment, yet additional spending is increasingly difficult to accommodate. Recent increases in health care spending also suggest that the slowdown observed over the past decade may not persist.1 In this context, the critical question for policymakers is not whether but how spending growth over the next decade can be constrained. We argue that 5 interconnected forces will shape not only how much the US spends on health care, but also who bears those costs and whether health gains are achieved in return.

The United States spends more on health care than any other country, yet its fragmented financing structure masks the full financial burden that individuals bear through taxes, premiums, and out-of-pocket payments. A sizeable number of people contribute to the health care financing of others while they themselves remain uninsured. This cross-sectional study used 2023 Current Population Survey Annual Social and Economic Supplement data to quantify health care contributions among US tax filers, by income quintile, payment type, and sociodemographic characteristics. Although total contributions were higher at each successive income quintile, out-of-pocket spending fell disproportionately on lower-income and sicker people. Uninsured tax filers younger than age sixty-five contributed approximately 64 percent of what their insured counterparts paid, despite lacking coverage. Virtually all tax filers contributed to US health care financing through its public financing streams, yet many remained exposed to significant financial risk or lacked coverage altogether. This reflects the fragmented structure of US health care financing, where financial contributions are not aligned with coverage or protection from medical costs.

Health systems face financial pressures as populations age and economic growth slows, with implications for who pays for health care and for what drives expenditure growth.