The Social Security program faces a longstanding financing shortfall that, if left unaddressed, would slash millions of retirees’ crucial monthly benefit payments in just eight years.

The deteriorating financial outlook for the retirement program, which supports roughly 61 million Americans, was released in its annual trustees report on Wednesday. It is now expected to run out of money nine months earlier than previously projected, which means benefits could be reduced by 23 percent if Congress does not act to bolster the program.

That puts the Social Security Old-Age and Survivors Insurance Trust Fund, which pays retiree and survivor benefits, on schedule to be depleted in 2033, or when today’s 59-year-olds turn 67. At that time, the program will have enough revenue coming in to pay only 77 percent of total scheduled benefits.

The most recent setback was driven largely by a policy change, known as the Social Security Fairness Act, which took effect in January and increased benefits for about 2.8 million government and public sector workers. But there were other factors: Government actuaries now assume that the birthrate will remain lower for longer, while projecting that workers’ compensation would weaken over time as they capture a lower share of the nation’s economic output.

A separate trust fund, which finances Social Security disability benefits for an additional 8.2 million people, is on more stable ground. It will be able to pay all of its bills through 2099, the report said.

The trustees also reported a slightly weaker financial outlook for the trust fund that finances hospital care for Medicare beneficiaries. They expect that that trust fund will be unable to pay all its bills in 2033, three years sooner than it had estimated last year. That change was driven mostly by increased spending on hospital care in 2024, a shift the trustees believe will continue into the next few years.

In their report, the trustees urged lawmakers to address the shortfalls in a timely way so that any changes could be phased in gradually, giving workers and beneficiaries time to adjust.

“Implementing changes sooner rather than later would allow more generations to share in the needed revenue increases or reductions in scheduled benefits,” the trustees said in the report.

Some policy experts say it’s hard to fully project Social Security’s outlook because the latest report doesn’t reflect many of President Trump’s policies, including his tariff and mass deportation plans, which are expected to worsen the program’s deficits.

“The most important story is not in the report,” said Kathleen Romig, director of Social Security and disability policy at the Center on Budget and Policy Priorities, who noted that the report’s economic assumptions were locked in at the end of last year. “The world has changed dramatically since then.”

If the administration’s tariffs cause the economy to contract and lead to job losses, that would dampen trust fund revenues because fewer payroll taxes would be flowing to the fund. If tariffs caused price increases, that could lead to a higher cost of living adjustment for Social Security recipients and therefore a bump in benefits. Immigrants, both lawful and otherwise, are generally a net positive to the trust fund. One analysis, from October, projected that Mr. Trump’s proposals would accelerate the trust fund’s insolvency by three years.

Social Security and Medicare have long faced a financing shortfall, partly because of demographic changes. Dwindling birthrates mean fewer workers are paying taxes into the programs, all while thousands of baby boomers are retiring daily and collecting their benefits for longer periods.

In addition, a larger share of the country’s wage base is not subject to payroll taxes, Social Security’s lifeblood, compared with years past. The taxes are applied only up to $176,100 in income, and rising income inequality means a greater share of Americans’ earnings exceeds that cap and is not taxed.

Mr. Trump has vowed to protect Social Security benefits, but he hasn’t introduced any proposals to shore up its financing. He empowered Elon Musk’s Department of Government Efficiency, known as DOGE, to embed at the agency, where it enacted aggressive federal job cuts and policy changes at a time when beneficiary claims were at a record high and staffing was already thin. The changes threw the agency into chaos, left retirees nervous and confused, and overshadowed its true challenges.

Mr. Musk, who recently left Washington amid a blowup with Mr. Trump, had cast his efforts to root out waste and fraud as a way to preserve Social Security. “As a result of the work of DOGE, legitimate recipients of Social Security will receive more money,” he said on Fox News in March.

But those kinds of efforts would have a minimal effect on a program that is already efficiently run, policy experts said, with overhead costs of half a percent of its total spending, and an improper-payment rate of 0.3 percent.

“To even suggest that it is possible to solve the fiscal challenges faced by Social Security focusing only on fraud, waste and abuse is misleading at best and dishonest at worst,” said Jason Fichtner, who held several senior positions at the Social Security Administration after being appointed by former President George W. Bush.

To put the magnitude of the financing shortfall in perspective, the trustees noted that revenue would need to rise by an amount that would raise the payroll tax by 3.65 percentage points. That would keep the combined retirement and disability trust funds solvent for the next 75 years, and bring the total tax to 16.05 percent.

In many cases, workers split the payroll tax burden with their employers; each currently pays 6.2 percent on earnings up to $176,100, for a total of 12.4 percent. By law, Social Security (unlike parts of Medicare) cannot use money from the federal budget’s general revenues to pay benefits.

Reducing all beneficiaries’ payments by 22.4 percent would also close the financing gap, but proposals to shore up Social Security often combine different approaches to varying degrees. “There are many variations on these options, including those that vary the timing, magnitude, and other specifics of the changes under consideration,” the trustees said in the report.

Republican-led proposals have historically suggested cutting benefits by raising the retirement age, among other changes. Democrat-led proposals typically support raising taxes.

Government actuaries have estimated that fixing Medicare’s trust fund over the long term would also require significant changes. To make sure Medicare had enough money to pay all its bills over the long term, Medicare would need to either reduce its overall spending on hospital care by 9 percent or lawmakers would have to raise the payroll tax that funds it to 3.32 percent from 2.9 percent, according to the report.

Neither option is under discussion by Congress, and Mr. Trump has vowed not to touch the program. A major bill working its way through Congress would cut Medicaid and other social safety net programs, but make almost no adjustments to Medicare.

Unlike Social Security, not all of Medicare’s bills are financed through a dedicated trust fund. Payments for the parts of Medicare that cover doctors visits and prescription drugs are funded through the government’s general fund and with premiums paid by beneficiaries. But the trustees did note that those costs are also expected to rise substantially, putting pressure on the federal budget. Many baby boomers will reach old age over the next decade, meaning they are likely to need more medical care.

Myechia Minter-Jordan, the chief executive of AARP, called on Congress to stabilize the social insurance programs, given their widespread support.

She added: “Older Americans nationwide consistently say that the future of Social Security and Medicare are the issues they care about most, and they stand ready to hold politicians across party lines accountable to strengthen these programs for the long term.”

Nicholas Nehamas contributed reporting.