The purpose of disability insurance is to replace the lost income from work should you become disabled, and unable to work. The disability insurance policy will stipulate when you are eligible to begin receiving benefits. Usually, you must be unable to work for a specified amount of time before disability benefits begin to be paid to you. The amount of the payments, the duration of coverage, and a description of exactly what constitutes a disability are contained in the policy. The premium for the policy is determined by a number of factors, including: the amount of the income payments, the length of payments, exactly what constitutes a disability, and such personal risk factors as the state of health and type of employment of the insured.