Many seniors travel extensively once they retire. And it makes sense -- when you're working and only have a limited amount of vacation time, trotting across the globe is easier said than done. But when you don't have a job to report to, you're free to jet off for weeks or even months at a time, provided you have the savings to do so.

When you plan your travel, you probably know to account for expenses like airfare, lodging, food, and activities. But there's one expense you might be overlooking: travel insurance.

Why seniors need travel insurance

Travel insurance serves a number of key purposes. First, it can protect you if something goes haywire in the course of your travels, whether it's a delayed flight or a problem with your hotel reservation. Travel insurance can also provide reimbursement if your luggage is lost, stolen, or damaged -- a somewhat common occurrence.

Smiling senior couple out on a body of water

Image source: Getty Images.

But perhaps the most important type of coverage travel insurance can give you is medical. If you're 65 or older and on Medicare, you should know that it won't cover healthcare issues that arise outside the U.S. Most Medigap plans won't cover health issues abroad, either. This means that if you get sick in the course of your travels -- or worse, are seriously injured -- you'll risk having to bear the entire cost of your care if you don't have insurance.

The good news is that travel insurance is remarkably affordable. A senior couple traveling to Greece for three weeks could get coverage for medical protection and evacuation of up to $1 million per person (with no deductible) for a mere $575. Of course, the amount you'll pay for travel insurance will depend on your age, destination, and the duration of your journey. The point is that spending several hundred dollars could save you many thousands if you are hurt or hospitalized in a foreign country.

When shopping for travel insurance, make sure the policy you buy comes with medical coverage -- including an emergency medical evacuation benefit. This way, if you encounter a health crisis abroad and need to be transported back to the U.S., an emergency evacuation that could otherwise cost tens or even hundreds of thousands of dollars will be covered.

Another option if you're 65 or older is to sign up for a Medicare Advantage plan instead of sticking with traditional Medicare. Many Advantage plans offer health coverage overseas, so if you plan to travel a fair amount in retirement, it could be worthwhile.

Otherwise, be sure to factor in the cost of travel insurance as you plan your various trips. A few extra hundred dollars here and there could spell the difference between escaping an overseas medical emergency debt-free or having your finances irreparably damaged for the rest of your life.