Not long. First of all, your physician needs to prescribe the therapy, and periodically needs to review your continuing need for it. But no matter how much therapy your doctor prescribes, Medicare will only pay a limited amount. Once you have paid your yearly Part B deductible, Medicare Part B pays 80 percent of the amount it approves for the therapy; you have to pay the remaining 20 percent out of your pocket, unless you have other insurance such as a Medigap policy. And there is a cap on the total amount Medicare will pay per year for physical therapy; in 2008 it is $1,810. After Medicare has paid that much, it will pay no more regardless of whether your physical therapy is medically necessary and prescribed by your doctor. After the first of the year, a new total amount will be available to you (slightly higher than the 2008 figure).
One way around this limit may be to get some additional therapy from an occupational therapist rather than a physical therapist. Although the name occupational therapy suggests that it is connected to work, in fact occupational therapy helps people who have had serious injuries, surgeries or illnesses to learn safe ways of doing everyday tasks – like walking, getting in and out of bed, lifting things, etc. It is offered by specially trained therapists and is considered by Medicare to be different from physical therapy, and has its own separate $1,810 yearly limit. If your doctor agrees that occupational therapy would be useful for you, the doctor can give you a separate prescription for it and Medicare can cover it in addition to your physical therapy.
To learn more about the rules of Medicare coverage for physical and occupational therapy, look at the Medicare publication Medicare Limits on Therapy Services.