Social Security's reserves are projected to run out in 2033, according to a new report, at which point the entitlement program's trust fund will be able to pay out just 77% of benefits to seniors.

That estimate is a year earlier than what was stated in the 2022 report for the Old-Age and Survivors Insurance (OASI) Trust Fund, according to the annual report released Friday from the trustees of the program. The revision reflects a 3% reduction in labor productivity and gross domestic product.

One bright spot: A projection for a key trust fund for Medicare is better. It's expected to exhaust its reserves by 2031, three years later than reported last year, after new data forecast lower health-care spending.

If the OASI was combined with the fund that pays out disability benefits — the Disability Insurance (DI) Trust Fund — the reserves would last a year more until 2034, when they could pay out 80% of benefits. But the two funds can't be combined unless there's a change in the law.

Both Social Security and Medicare face long-term shortfalls under currently scheduled benefits and financing, issues that politicians are finally starting to debate.

"This year’s Trustees Report reinforces the urgent need for Congress to shore up Social Security’s finances," Shai Akabas, director of economic policy at the Bipartisan Policy Center, told Yahoo Finance. "We have known this cliff was looming for decades, and yet every year, we delay taking action and the measures required to solve the problem get harder."

Social Security, which provides benefits to 66 million people, is mostly a pay-as-you-go program. Payroll taxes collected from workers now pay out the benefits to current recipients. For instance in 2019, 89% of the $1.1 trillion in Social Security revenue came from payroll taxes. The rest came from income taxes on Social Security benefits and interest earned on the government bonds held by the trust funds.

Part of the problem is that people are living longer and the birth rate is falling, so the ratio of workers to beneficiaries is shrinking.

Additionally, much of wage growth has gone to higher earners, reducing the percentage of wages subject to Social Security tax, administration officials said. In 1983, 90% of earnings fell below the maximum amount subject to Social Security tax. That’s down to 82%, officials said.

That means payroll taxes will contribute a smaller percentage to Social Security's revenues.

Right now, the fund’s reserves make up for that shortfall. For instance, the total cost of Social Security last year was $1.244 trillion, while revenue covered only $1.222 trillion, according to the report. The program tapped the surplus, which ended last year at $2.830 trillion, down from $2.852 trillion. That reserve is expected to run out in 10 years.