Been thinking about retirement lately and realized how many people I know are making the same mistakes with their planning. These wrong assumptions could seriously derail your golden years if you're not careful.

First one that gets people: assuming Social Security will actually cover your living costs. I get why folks think this—it's literally called Social Security, right? But here's the thing: if you're earning an average salary, those monthly checks replace roughly 40% of what you made while working. That means you're looking at a 60% lifestyle cut unless you've built up other income sources. Social Security is meant to be a foundation, not the whole house. You need to actually save money now—whether through a 401(k), IRA, or other vehicles—to fill that gap later.

Second assumption that catches people off guard: Medicare is free once you turn 65. I used to think this too until I dug into it. Yeah, you enroll in Medicare, but then you're paying Part B premiums, potentially Part D premiums for drug coverage, plus deductibles, copays, and coinsurance on top of that. And here's the kicker—Medicare doesn't cover dental or eye exams. So you need to actually budget for healthcare in retirement. If you can, max out a health savings account while you're still working. That gives you a dedicated pool specifically for medical expenses down the road.

Third one surprised me: the idea that you should dump all your stocks once you start living off your savings. A lot of people think retirement means going 100% bonds and cash for safety. But that's actually risky in a different way—you won't keep up with inflation. A 50/50 stocks-and-bonds split is pretty common among retirees, and some people even go heavier on stocks if they've got a couple years of living expenses sitting in cash as a cushion. The right portfolio allocation lets you capture market gains without going crazy with risk.

The common thread here? Don't let assumptions about retirement make your decisions for you. Get clear on what Social Security will actually provide, understand what Medicare really costs, and think carefully about your asset allocation. Maybe talk to a financial advisor to stress-test your assumptions against reality. Your retirement is too important to wing it.