The challenging part of retirement is adjusting to the idea of living on a fixed income. Many seniors, in fact, experience loads of stress over the notion of depleting their nest eggs prematurely. The better you plan for what retirement will cost you, however, the less likely you'll be to struggle financially during it. Here are a few big expenses that are likely to eat into your savings, so be sure to prepare for them appropriately.

1. Healthcare

Healthcare is some seniors' greatest expense. Even if you kick off your golden years in a relatively healthy state, you never know what medical issues might arise as you age. And Medicare often falls short in covering seniors to the extent they need it.

A senior couple sits at a table reviewing paperwork.

IMAGE SOURCE: GETTY IMAGES.

To avoid finding yourself cash-strapped later in life, expect healthcare to cost a bundle and save for it. HealthView Services, a cost-projection healthcare software provider, estimates that the average 65-year-old man today will spend $189,687 on healthcare in retirement, while the average 65-year-old woman will spend $214,565. That's a lot of money.

There are steps you can take, however, to lower some of your medical costs. First, consider a Medicare Advantage plan. An alternative to traditional Medicare, Medicare Advantage is an all-in-one health and drug plan, and it typically offers a wider range of coverage than original Medicare will give you. Another option is to look into supplemental insurance to make up for traditional Medicare's coverage gaps.

Being smart about your prescriptions can also help you keep your healthcare costs in check. Using generic drugs when possible can make your copays more manageable, as can ordering medications in bulk. And don't discount the possibility of snagging free samples -- medical offices get them all the time, and if you're not shy about asking, you can shave some money off your total costs that way.

2. Housing

Many seniors are surprised at what they end up spending on housing, especially since a large percentage enter retirement mortgage-free. But even if you do manage to shake that monthly mortgage payment in time for retirement, don't forget that as homes age, they tend to require more upkeep and repairs. And the older you get, the less physically capable you might be of performing that work yourself, thereby leading to an uptick in maintenance costs.

Another thing: Property taxes have a tendency to rise over time, even during periods when home values decline. Furthermore, all it takes is for your home to get assessed at a much higher value than previously determined, and bam -- your property tax bill could skyrocket.

Be prepared for the costs of homeownership in retirement, and save for them so you're not left in the lurch. Or consider renting, especially if you haven't yet paid off your mortgage.

3. Transportation

Many seniors assume that their transportation costs will drop drastically once they stop working. After all, not having to commute to work should save you a bundle, right?

Wrong. If you own a car, the bulk of the expense associated with it most likely isn't fuel costs, but rather the cost of insurance, maintenance, and repairs. In fact, AAA estimates that it costs $8,849 a year, on average, to own a vehicle, which is a pretty high number when your income is limited.

A better bet, therefore, might be to try to avoid owning a car in retirement. Granted, that may not be possible if you live in a suburban or rural area, but if you're in or near a city, relying on public transportation could save you quite a bit of money. Otherwise, try unloading one vehicle if you're currently a two-car household. That'll save you a bunch of cash, too.

4. Entertainment

The funny thing about work is that it's a relatively inexpensive activity. And when you stop having a job to go to, you might suddenly find that you're spending a small fortune to keep yourself occupied.

Even if you're not planning to travel extensively during retirement, all of those museum visits, theater tickets, and lunches with friends at local cafes could quickly add up. And while there are senior discounts out there that might minimize the damage, you should still make sure to budget for leisure in retirement. At the same time, make an effort to seek out free or low-cost entertainment to keep your spending in check. Many museums, for example, offer free admission days, and with a fairly flexible schedule, taking advantage should be feasible.

Even if you save efficiently for retirement, you might find that your senior living expenses are higher than planned. Prepare for these four in particular to avoid get caught off-guard later in life.