When 59-year-old James Morant was visiting Paris, he slipped in the tub at his hotel and cracked a rib. He was rushed to the American Hospital, where he was X-rayed and given pain medication. Though he had private health insurance back home, the hospital wouldn’t release him until he paid the $600 bill.

“I was, like, ‘You don’t understand—I’m a federal employee; I’m covered by Blue Cross Blue Shield!” says Morant, a senior advisor for international affairs at the Environmental Protection Agency. It didn’t matter. While he understood that the fee could’ve been worse, he was chagrined to pay anything at all.

Like Morant, most travelers never think to buy supplemental health insurance—particularly if they deem their destination a “safe” one with top medical care. But accidents can happen anywhere. And short-term insurance plans are inexpensive—typically only 5-8 percent of a trip’s total value, according to Vikki Corliss of InsureMyTrip.com, a travel insurance comparison website.

Rates depend on your age, trip length and destination. One basic two-week plan with Medex (medexassist.com) for a 35-year-old going to Sweden costs $56; for a 71-year-old, $80.50. That’s still less than $6 a day—for coverage of up to $100,000 with a $25 deductible (per medical emergency). For extra fees you can add an “adventure sports” rider and trip-cancellation and lost-baggage insurance.

Can’t decide? Here are some guidelines for when to buy a one-time health-insurance plan.

· You have no private health insurance—or you have a plan that doesn’t cover you overseas. Some private plans will partially reimburse medical expenses incurred outside the United States, but few cover medical evacuation back to the U.S. (Note: Except in rare instances, neither Medicare nor Medicaid provides coverage outside the U.S.)

· You’re visiting a developing country where medical care is unreliable. Some companies offer evacuation to the nearest appropriate medical facility. Most are also linked to a global network of English-speaking medical professionals. Medex subscribers can order a report on their destination that lists specific health risks and vetted hospitals (360m Global Medical Monitors; $9 each).

· Your plans include high-risk sports. Many travel health policies have an “adventure sports” rider that covers some extreme activities. Medex’s plan with a rider (TravMed Choice) costs from 20 to 30 percent extra, and is good for mountaineering, bungee jumping, scuba diving and caving. (Not covered: skydiving, hang-gliding or parachuting.)

· You have a chronic condition that may be exacerbated by travel or may require specialized care. Check that the plan covers pre-existing conditions, like asthma or high blood pressure. Travelex (travelex-insurance.com; 800-228-9792) will sometimes waive its pre-existing-conditions clause if you were considered “medically fit” at the time you purchased the plan.