There's a reason we're told to save as much of our income as possible for retirement. Social Security will only suffice in covering about 40% of the average worker's pre-retirement earnings. Most people, however, need a minimum of 70% of their previous income to pay the bills in retirement, and that assumes an extremely frugal lifestyle.

In fact, that 70% target has long been tossed around as the degree of replacement income to aim for, but in reality, most of us will need far more than that to cover our senior living expenses. Here are three in particular that could end up costing considerably more than you'd expect.

Older couple looking at bills

Image source: Getty Images.

1. Healthcare

Most seniors expect to spend a bundle on healthcare, but many of today's near-retirees are floored by the latest estimates of what medical needs in retirement might cost. According to HealthView Services, a provider of cost-projection software, the average healthy 65-year-old couple today will spend $377,000 on medical care in retirement. That's $188,500 a person, assuming you fall into the "healthy" category. If you don't, there's a good chance your costs will well exceed that figure.

2. Housing

The average retiree spends $15,528 a year, or $1,294 a month, on housing, but if you're among the 30% of homeowners who enter retirement with mortgage debt, your costs might climb even higher. Even if you're only making mortgage payments during your first few years of retirement, those extra withdrawals from savings could eat away at your nest egg at an alarmingly fast pace.

Furthermore, if you're going to hold onto your home in retirement, it's fair to assume that over time, your maintenance expenses will increase. The typical homeowner spends 1% to 4% of their home's value on annual upkeep, but even if you start out around that 2% or 3% mark, there's a good chance you'll hit the high end of that range at some point during retirement. And if your home is worth $500,000, which could easily be the case in a more expensive part of the country, spending 1% more each year on maintenance translates into an additional $416 per month.

3. Long-term care

Here's some bad news --  that healthcare expense figure doesn't include the cost of long-term care, which an estimated 70% of seniors will need. Not only will most retirees require some type of long-term care, but the costs could be downright catastrophic depending on what that care actually entails.

According to current estimates, it costs over $43,000 per year to reside in an assisted living facility. Nursing home care, meanwhile, will set you back over $82,000 a year if you're willing to bunk with a roommate. While long-term care insurance can help defray these costs, you'll still need to be prepared for whatever portion of that burden ultimately falls on you.

Step up your savings game

Now that you're more aware of the costs you might face in retirement, it's time to ramp up your savings so that you're better equipped to cover them -- because most older workers don't have enough savings to even come close. The average household nearing retirement has $163,577 put away. Over a 20-year period, that's just $8,178 of income per year, which won't even suffice in covering medical care for a single individual. Furthermore, it's estimated that over 40% of older households have no retirement savings at all. Unless you want to resign yourself to a perpetually cash-strapped existence, you'll need to build up your nest egg while you still can.

For starters, work on maxing out your retirement plan contributions, or getting as close to doing so as possible. If you're over 50, you can put up to $24,000 a year into a 401(k), or $6,500 a year into an IRA. Contributing just $5,000 a year to either account over a 10-year period will give you $63,000 more to work with in retirement, assuming your investments generate a moderately conservative average annual 5% return.

Along these lines, you might consider postponing retirement for a few years to give yourself time to build up that nest egg. Not only will working longer offer more savings opportunities, but it'll also help you hold off on tapping whatever limited savings you have.

Finally, you might consider rethinking your retirement plans so that your lifestyle aligns with your savings level. If you don't have much of a nest egg, you may need to downsize your living space, move to a more affordable neighborhood, or look into part-time work to compensate.

No matter what you do, don't make the mistake of underestimating the cost of healthcare, housing, and long-term care in retirement. Otherwise, you could wind up in a bad situation at the most vulnerable time of your life.