New York (CNN) In 16 years, Social Security will have to cut benefits by 21% if lawmakers do nothing to cure the program's long-term funding shortfall.

That's what the Social Security and Medicare trustees projected in their 2018 annual report released Tuesday.

The trustees estimate that by 2034 the combined trust funds for Social Security — which help fund the old age and disability programs — will run dry. At that point Social Security will be able to pay only 79% in promised benefits to retirees and disabled beneficiaries.

Those projections are roughly on par with last year's report , which estimated the combined Social Security trust funds would be tapped out by 2034 and would then only be able to pay out 77% of benefits.

For the first time since 1982 Social Security's costs will exceed its payroll income plus interest from the $2.9 trillion trust funds. That means it now must start drawing down principal in the trust fund to continue paying promised benefits in full.

The forecast for Medicare, meanwhile, is a bit worse than last year's.

The trust fund for Medicare Part A, which covers hospital and nursing home costs for seniors, would run dry by 2026, three years earlier than last year's projection. At that point the program would only be able to pay out 91% of promised benefits.

Before the Affordable Care Act was passed, the trustees had projected the Part A trust fund would run dry this year.

Meanwhile, Medicare Part B, which helps seniors pay for doctor's bills and outpatient expenses, is funded by a combination of premium payments and money from general federal revenue. The same is true of Part D, which offers prescription drug coverage. Both will be financed in full indefinitely, but only because the law requires automatic financing of them. Their costs, however, are scheduled to grow from 2.1% of GDP in 2017 to 3.6% in 2037.

Congress has punted on the issue of shoring up the solvency for both entitlement programs for years. And this year likely won't be any different, with lawmakers focused on navigating the Trump era and planning for the mid-terms in November.

To ensure both Social Security and Medicare remain solvent for decades to come, they have three basic choices: they can raise the payroll taxes paid into the programs by both employees and employers, they can cut benefits for some or all beneficiaries, or they can do some combination of the two.

As an extreme example, to make Social Security fully solvent over the next 75 years, the payroll tax rate would need to be increased permanently to 15.18% from 12.4% today. Or benefits could be cut by 21% for those who become eligible this year or later, said Tim Shaw, a senior policy analyst at the Bipartisan Policy Center.

Instead any changes made will have to balance who can best afford to pay more or receive less, and how much time they're given to adjust to those changes.

In all cases, however, the longer lawmakers wait, the more dramatic and abrupt the changes will have to be.

—CNN's Donna Borak contributed to this report