If you need it, then right now! It will never be cheaper for you than it is right now because the cost of long-term disability insurance increases with age (because the risk of disability also increases with age). If you're in good health, you should easily qualify for a policy - and can lock in better rates at this age with a non-cancelable policy. Usually, people think about disability insurance after their health takes a turn. But that's often too late.If your health declines, you may no longer be insurable at an affordable premium.