Change in length for a stress higher than the yield stress?

I know that when a specimen is under stress in the elastic region of its stress strain curve, the change in length is F*L/A*E (force times length over area times elastic modulus) or stress*L/E. But what happens if it is under a higher stress than the yield stress, yet lower than the ultimate stress, and then the stress is released. I know that it not return to its original length, but how do I determine the change in length. Do I still use the same formula stated earlier?