The trustees of the Social Security system’s finances released their annual report on Wednesday afternoon. They say the combined trust funds that help pay old age and disability benefits are likely to run out by 2034, the year when today’s 48-year-olds reach full retirement age. The trustee’s estimate reflects the latest economic and demographic projections, and it changes a bit most years. Last year’s estimate for trust fund depletion was 2033. But what does it mean to say the Social Security trust fund has run out? Let’s be clear: Social Security benefits won’t disappear entirely when that happens. If nothing else changes, the payroll taxes still being paid by younger people in the workforce will be enough to fund about 79% of scheduled benefits, says the report. That’s because Social Security is by and large a pay-as-you-go system. At the individual level is looks a bit like a savings account, where you contribute money now in order to draw it down after you stop working. But in fact, it’s never been primarily run on saved money. Taxes from today’s workers are used to fund the benefits of today’s retirees. But after the system was overhauled in 1983 and up until 2010, the amount of payroll tax dollars flowing into the system was higher than the amount of money that was needed to fund benefits. That extra money is in the so-called trust fund, and it’s invested in special, untraded Treasury bonds. Thanks to interest from the Treasuries and taxes on higher-earning beneficiaries, the Social Security system still takes in a bit more money than it pays out each year. But soon that will flip over and Social Security will have to start eating into its past surplus to pay beneficiaries—and 2034 is the year that the surplus is currently expected to run out. When that happens, unless Congress intervenes, the Social Security administration will be able to pay only the benefits supported by current Social Security taxes. The trustees warned that a similar moment of reckoning could be coming much sooner for those who get Social Security disability payments. The trust fund that specifically supports disability insurance is scheduled to run out next year. In the past, Congress has addressed such problems by moving money from the much bigger retirement system into disability, but many Republicans in Congress are saying they want changes to disability-insurance rules before they’ll do this. Returning to the system as whole, obviously a sudden drop to 79% of benefits is no trivial thing. It would be a brutal cut for many retired people who rely on Social Security. The point is that addressing a funding shortfall isn’t as challenging as stopping the system from going all the way to paying zero. All told, the gap between what Social Security promises to pay and what it will collect amounts to about 1.2% of GDP in 2035. That’s serious money, but also a fixable problem (except for the politics). For context, over the next decade, annual spending on everything besides Social Security and health care programs is projected to shrink by 1.7%, according to the Congressional Budget Office. Sign up for and more view example Proposals to keep Social Security on track for the longer term range from promising to pay less—by further raising the retirement age, or adjusting benefit formulas—to raising taxes on higher earners or wealthier beneficiaries. Think of 2034 as the rough political deadline for Congress to work that out, although the sooner it does so, the more gradual changes can be for either beneficiaries or taxpayers.