Many people get motivated to save by thinking about the possibility of early retirement. But once they start thinking about actually quitting their jobs a few years early, one huge challenge often rears its ugly head.

If you save as much as you can and invest it well, you'll put together a nice nest egg for your golden years. But if you're thinking about early retirement, you face an additional obstacle: making sure you have the affordable health insurance coverage you need.

Say goodbye to employer coverage
Health insurance is a big problem for those who retire early because many companies, including Verizon (NYSE: VZ) and Caterpillar (NYSE: CAT), have scaled back on providing coverage for retirees. And others that had retiree health insurance in the past, such as Union Pacific (NYSE: UNP), aren't offering such coverage to new workers.

The trend is likely to continue, as companies with bloated pension obligations look for ways to shift costs to become more competitive. GM (NYSE: GM) and its agreement to transfer responsibility for health-care-related costs to the United Auto Workers union may become a model for companies in other industries trying to reduce expenses.

Running the gantlet
The lack of employer coverage means that early retirees face the prospect of paying for their own health care costs for years, until Medicare kicks in at age 65. While workers can elect continued coverage from their employers' health insurance under COBRA, premiums can be extremely expensive, especially since employees are usually responsible for the full cost. Furthermore, COBRA coverage can end in as little as 18 months, therefore failing to close the gap entirely for many early retirees.

With the baby-boom generation approaching retirement, insurance companies have started to market health-insurance policies to help bridge the gap between early retirement and Medicare eligibility. Humana (NYSE: HUM) and WellPoint (NYSE: WLP) have or are planning policies tailored to early retirees, while Aetna (NYSE: AET) is teaming up with AARP to offer coverage to members over 50.

Even as more products come to market, prospective early retirees shouldn't expect any bargains. Health insurance costs generally rise dramatically with age, so those in their early 60s are especially vulnerable to high premiums.

Be prepared
The challenges of health insurance shouldn't keep you from retiring early. You just have to make sure you don't ignore the costs involved. Going without health insurance can be devastating to your finances if you get sick, so you'll want to iron out how you'll obtain the coverage you need before you hand in your letter of resignation.

For more about the issues retirees face, read about:

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Fool contributor Dan Caplinger already worries about health-insurance costs. He doesn't own shares of the companies mentioned in this article. The Fool's disclosure policy never quits on you.