Saving for retirement isn’t just about stashing away however much you think you’ll need to keep up your lifestyle — it includes planning for the unknown.

Unfortunately, a lot is unknown. For millennials, that includes if they’ll receive Social Security or Medicare benefits, if they’ll need to help their aging parents, and how their retirement funds are managed. “The need for millennials to save for retirement as early as possible is even greater now,” said David Siegel, chief executive of investing website Investopedia.

More than half (52%) of millennials guessed how much they would need in retirement, according to a 2014 Transamerica Center report, and only one in 10 used a calculator or spreadsheet.

Already, millennials are in a tough spot — they have more student debt than any generation before them, they earn less money than the generations before them did at their age and they’re in a “sandwich” generation, where they’re likely going to have to support themselves, alongside their parents and their children. Millennials are also not very optimistic about their retirement — 64% of respondents in a Wells Fargo survey of more than 1,000 millennials said they would never accumulate $1 million in savings over their lifetime. They also expect to work until they’re 90, according to a video by research firm Morningstar.

See: Millennials need to put on gloves and fight now for their retirement

The good news? It’s never too early to save, and the quicker a millennial begins, the better their chances of being comfortable in retirement. Experts suggest starting with whatever they can muster, even as little as $5 every month. The benefits of such a small amount will add up with compound interest, but doing so also forms a habit of putting away money consistently, and the next time they get a raise or a little extra money, they should continue to add more to their savings. Overall, despite the financial hurdles, millennials are confident in how they save.

Still, it never hurts to be overly cautious, and that includes saving more or planning for one of these four situations to occur:

You don’t get Social Security

Millennials aren’t all that confident they’ll receive Social Security benefits in the future, according to a recent Investopedia survey: 19% said they felt confident whereas 81% were not. Right now there is a lot of debate about what to do with the Social Security program, which can start for people as early as 62 years old. Anne Alstott, author of “A New Deal for Old Age” and a Yale Law School professor, thinks the age to receive full benefits should increase to 76, because people are living healthier for longer and working into their retirement age. Doing so might even keep Social Security alive for millennials, when the time comes. Until a solution is reached, however, Siegel suggests millennials begin saving for that hole now.

You have to take care of your aging parents

More than a third of Americans believe they will help their parents financially in the next seven years, according to the Society of Grownups, an online financial advice group. One 21-year-old Reddit user is already planning to get started helping her parents with their retirement, because they always supported her and were paying down a mortgage. Experts suggested showing the parents how to open a health savings accounts as an investment portfolio as well as saving for medical expenses. They also suggested helping contribute to Roth Individual Retirement Accounts, and paying the taxes from an IRA-to-Roth-IRA switch.

Unexpected health-care costs

More than half (60%) of respondents over 50 years old said they were worried they would have to delay their retirement, possibly because of the impact of government policies or a lack of savings to cover health-care costs, according to the Investopedia report. This can serve as a lesson for millennials. Health-care costs might be dangerously underestimated — today, a couple might need $350,000 to pay for most of their health-care costs. Not everyone can afford their health care — more people have had trouble paying for their health insurance since 2015, according to the Kaiser Family Foundation, and they’re putting off taking care of themselves: 27% of the public said they or a family member have delayed necessary health care because it was too expensive, with another 23% saying they skipped a medical test or treatment and 21% didn’t fill a prescription.

Your employer or adviser is mismanaging your retirement funds

Mismanagement of funds or too many fees on your retirement accounts could be detrimental to the number you see when it comes time to retire. The government created the fiduciary rule — now delayed — intended to combat excessive fees and foster more transparency in retirement investments management. Former President Obama and the Labor Department said retirement savers lose $17 billion a year to conflicts of interest in their investment advice — savers are urged to review the details of their accounts.

Millennials need to worry about these 4 things — in addition to saving for retirement