The United States may be operating on a shrinking fiscal timetable, according to economist Kent Smetters, who argues that rising debt levels and an ageing population are creating pressures that future generations will struggle to absorb.
Smetters, faculty director of the Penn Wharton Budget Model, believes the country’s debt trajectory is increasingly tied to long-term spending commitments that disproportionately benefit older Americans. Speaking to Fortune, he warned that policymakers may have roughly two decades before the nation’s fiscal position reaches a point where corrective action becomes significantly harder.
His concern extends beyond debt figures alone. Smetters argues that successive generations have had political incentives to defer difficult choices by pushing costs into the future, creating a system where current voters receive benefits while future taxpayers inherit the burden.
A 20-year window before debt reaches dangerous territory
According to Penn Wharton’s modelling, US federal debt has an upper sustainable boundary of approximately 210% of gross domestic product. Smetters describes this figure as a mathematical limit rather than a prediction, arguing that investors would eventually refuse to finance borrowing at affordable rates if debt rose beyond that threshold.
The timeline could arrive sooner than many expect.
Under assumptions that healthcare spending continues to outpace broader economic growth, the model suggests the US could reach this limit within around 20 years. There is also a one-in-four probability that fiscal capacity could be exhausted in as little as 14 years.
The model identifies a “closure year”, the final point at which policymakers could restore sustainability through feasible tax adjustments. Depending on healthcare spending trends, that deadline could arrive as early as 2045, or around 2051 under more optimistic scenarios.
Smetters said financial markets are currently pricing government debt on the assumption that Congress will eventually act.
“The assumption is that the financial markets are being set in a way where they keep believing that Congress will eventually get its act together up until the point where it’s mathematically impossible for that to be true anymore,” he told Fortune.
He added that investor confidence could shift unexpectedly, making market instability difficult to predict.
At the centre of his argument is federal spending allocation. He said the government spends roughly ten times more per older person than per younger person. In aggregate, spending on older Americans is approximately six times higher than spending directed towards younger generations.
Penn Wharton estimates that Americans aged 65 and over receive $2.7 trillion annually, equivalent to 38.6% of total federal spending and nearly 62% of age-related expenditure.
Social Security deadlines are approaching quickly
Smetters also pointed to Social Security as a looming test of Washington’s willingness to act before a crisis emerges.
The main trust fund supporting retirement benefits is projected to be depleted in the early 2030s, a timeline that now broadly aligns with estimates from both the Social Security Trustees and the Congressional Budget Office.
Once reserves are exhausted, benefits would only be payable at roughly 83% of scheduled levels, with that percentage gradually declining over time if reforms are delayed.
Smetters said history suggests lawmakers may postpone action until pressure becomes unavoidable.
“The last time we fixed Social Security in 1983, we waited very close for bad things to happen,” he said.
He was also sceptical that newer ideas, including technology-driven “AI dividends”, would provide a meaningful solution. Higher economic growth alone, he argued, does not automatically solve fiscal imbalances because government spending often rises alongside expanding economies.
Instead, he has advocated redirecting tax expenditures currently attached to retirement savings incentives. He has previously proposed eliminating tax deductions for 401(k) and 403(b) contributions and using those resources to establish retirement accounts for lower-income workers connected to earned income tax credits.
Debt crises rarely stay confined to economics
The broader concern extends beyond government accounting.
Historical examples show that prolonged fiscal stress can reshape politics, undermine institutional trust and create fertile ground for populist movements. Countries facing severe debt problems often experience social consequences that outlast the financial crisis itself.
The UK offers a recent warning. Smetters pointed to former British prime minister Liz Truss, whose proposed unfunded tax cuts triggered a sharp market reaction in 2022 and rapidly ended her premiership.
Additional context also suggests demographic trends will intensify the debate. According to projections from the US Census Bureau, Americans aged 65 and older will continue to represent a larger share of the population over the next two decades. That means programmes such as Social Security and Medicare will consume a growing proportion of federal resources even without significant policy expansions.
This creates a difficult balancing act. Younger workers will be expected to support a larger retired population while also managing their own housing, education and healthcare costs.
What investors and policymakers should watch next
The immediate danger is not an abrupt default but a gradual erosion of confidence.
Bond investors may begin demanding higher returns well before debt reaches its theoretical limit, increasing borrowing costs across the economy and reducing policymakers’ room for manoeuvre.
The next decade will therefore be defined by whether Congress can agree on long-term reforms before markets force the issue. Social Security funding decisions, healthcare spending controls and tax policy changes will all become increasingly important.
The underlying message from Smetters is straightforward: fiscal problems compound quietly for years, until they suddenly become impossible to ignore.
