Don't let this huge expense derail your retirement plan. Photo: Louise Docker via Flickr.

At least 70% of people over the age of 65 will need long-term care in their lifetime, according to the U.S. Department of Health and Human Services

Just let that sink in for a moment. Even if you're in great health now, odds are you'll need long-term care at some point. Have you planned for it? You should, because it could be one of the biggest threats facing your retirement.

The cost of long-term care
Long-term care is far more expensive than many people realizeAccording to Genworth Financial, in California, the average cost for a day healthcare facility is about $20,000 per year, while a home health aide costs an average of $53,000 and the average private nursing-home room costs over $100,000 annually. (Use Genworth's online map to find data for your state.)

In other words, if you or your spouse should suddenly need long-term care, you'll be facing additional expenses that could outstrip what most Americans earn in a year. That's on top of your usual living expenses. The cost can become completely unmanageable before you even know what's happened.

Consider insurance
If you don't have a significant asset base, you should consider long-term care insurance, especially given that health insurance plans generally cover limited types and dollar amounts of long-term care. For example, most health insurance will only cover up to 100 days of skilled nursing that follows a recent hospitalization for a related condition. That means you're on the hook for the rest.

From this perspective, long-term care insurance starts to look really attractive, especially considering that seven out of 10 Americans could make use of it.

If you're thinking of buying a policy, then don't delay. The older you get, the more expensive you are to insure, therefore stalling defeats the purpose of the insurance. And if your health takes a turn for the worst, you may be ineligible for coverage. In fact, 45% of long-term care insurance applicants are denied coverage. That number rises to 66% for those 80 and over. So, even though it's an extra cost now, getting a policy while you're relatively young and healthy could pay huge dividends later on when you really need it. 

Another benefit of buying a long-term care policy is that it makes you eligible for tax deductions. These tax breaks won't eliminate the cost, but they certainly make a decade or two of insurance premiums less painful.

Long-term care can quickly eat up retirement savings. Take the time to plan for it so that if the need arises, you won't be scrambling for a solution. Depending on your situation, insurance could well be the ticket.

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.