One in 4 adults will become disabled at some point before reaching retirement age, according to the Social Security Administration. Yet few people prepare for the possibility that any one ailment could cause them to miss work for an extended period of time. A total of 20.1 million adults of employment age report a work disability, according to research published by the National Institutes of Health. Common causes include back or neck problems, depression, anxiety or other emotional issues as well as arthritis or rheumatism. "Most disabilities you can't even see," said Leston Welsh, the head of disability and absence management at Prudential Group Insurance.

Most disabilities you can't even see. Leston Welsh head of disability and absence management at Prudential Group Insurance

There are two basic kinds of insurance that can protect you financially if you are unable to work: Policies for short-term disability, which maternity leave is typically covered under, generally replace 60% to 70% of your base salary. Long-term disability, which ordinarily kicks in after three to six months, typically replaces 40% to 60% of your income. "Understanding both short- and long-term disability coverage options is one of the most important ways individuals can protect themselves, their families and their finances," said Bill Smith, the president of Cigna Group Insurance.

Most workers have no disability coverage

About three-quarters, or 78%, of employers offer short-term benefits to their employees, according to a survey by the International Foundation of Employee Benefit Plans. Sixty-three percent also offer long-term disability benefits to their workers. However, only 38% of all workers take advantage of short-term disability insurance and just 33% opt for long-term insurance. Only five states have statutorily mandated disability benefit plans that include limited coverage similar to short-term disability. More from Invest in You:

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What millennials need to do now to retire rich someday As a result, more than half of people who experienced a disabling event took more than two years to recover financially, according to a separate disability study by Cigna. "You are not only dealing with medical bills but lost wages and income," Cigna's Smith said. Altogether, about 50 million working adults in the U.S. don't have any disability insurance other than the basic coverage available through Social Security. But the average SSDI benefit is only about $1,200 a month, or $14,000 a year — barely above the poverty line.

Hard to qualify

In addition, the requirements to qualify are rigorous. Your condition must be so severe that it will keep you from working for 12 months or more. In addition, there is a significant lag time before the benefit kicks in – even up to two years – which means you must have other coverage or a well-padded emergency fund to bridge the gap. For all of those reasons, "if your employer offers something, you should consider it," said Mike Stein, a senior financial analyst at Allsup, a company that helps people file and receive benefits. (Workers at or near retirement age may be offered short-term disability or long-term disability through an employer; however, long-term disability benefits could be limited.)

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