When we think about retirement, many of us are wired to assume that our costs will naturally drop as a result of no longer working. But we may be overestimating the extent to which that might happen. While it's true that some expenses, like commuting, go down in retirement, others are, in fact, likely to climb. Here are five in particular that tend to catch retirees off guard.

1. Healthcare

Healthcare is probably the one expense with a higher tendency to go up rather than down in retirement. That's partly because Medicare has its limitations, and countless seniors are forced to pay for a wide range of services that may have been covered during their working years. According to recent projections, the average healthy 65-year-old couple today will spend a whopping $400,000 or more on medical costs in retirement. Reading between the lines, if you're not particularly healthy, you can, and should, expect to see that number climb even higher.

Older man on a laptop with serious expression

IMAGE SOURCE: GETTY IMAGES.

2. Housing

Though housing doesn't always go up for retirees, it can be a pricier prospect than anticipated. Even if you're among the 70% of seniors who manage to pay off their mortgages in time for retirement, you can't forget about the peripheral costs of homeownership, such as property taxes and maintenance. In fact, property taxes actually have a tendency to rise over time, even during periods where the housing market itself underperforms. Furthermore, it costs the average homeowner 1% to 4% of his or her home's value to keep up with maintenance each year. Since retirees tend to own older properties, you may inevitably wind up hitting the highest end of that range, which could throw your budget off-track.

3. Entertainment

When you're not spending 40 hours or more at the office each week, it stands to reason that you'll need to get creative and find ways to fill that newfound free time. And while you don't necessarily have to spend a bundle on travel and leisure, you should by no means count on your entertainment costs going down once you stop working. In fact, you'd be surprised at how a few discounted museum entries and movie tickets a week can really add up over the course of a given year. It's estimated that 58% of workers fail to account for leisure spending in retirement, so rather than discount the amount you'll spend, factor it into your budget.

4. Taxes

Contrary to what many retirees are led to believe, taxes can constitute a significant financial burden during retirement. Not only will you pay taxes on withdrawals from a traditional 401(k) or IRA -- withdrawals that you're actually required to start taking upon reaching age 70 1/2 -- but you'll also pay taxes on traditional investment income, interest on money in the bank, and, in some cases, a large chunk of your Social Security benefits.

Now the good news is that you do have some options for lowering your taxes down the line, whether it's moving your savings from a traditional retirement plan to a Roth account, or shifting some investments into municipal bonds, which always offer federal tax-exempt interest payments. But if you don't adopt some sort of tax-saving strategy, you may come to find that you're losing a huge portion of your retirement income to taxes alone.

5. Long-term care

While you may not necessarily picture yourself living out your senior years in a nursing home or specialized facility, a staggering 70% of seniors wind up needing some type of long-term care. And if you don't save enough to cover those costs, or get yourself a comprehensive insurance plan, you may be in for a shock during retirement.

According to recent projections, it costs over $82,000 a year to reside in a nursing home, and that's for a shared room -- a private one will set you back upward of $90,000 annually. Furthermore, the average assisted living facility charges more than $43,000 per year. If you don't read up on these costs and come up with a game plan for covering them should they arise, you may be in for a world of financial shock at a time.

Underestimating your senior living costs could be one of the greatest retirement mistakes you'll ever make. Rather than take your chances, read up on how seniors today are spending their money, and see how well your savings are likely to stack up. You may need to adjust your current retirement plan to ensure that you don't run short on money later in life.

The Motley Fool has a disclosure policy.