An algorithmic approach is presented for determining the necessary open-loop back-offs from a steady-state optimum, so as to ensure that disturbances cause no constraint violation. The approach consists of defining a joint optimisation-flexibility problem that can be solved within an optimisation framework based on a cutting-plane approach. After calculating the open-loop back-off cost over the disturbance range of interest, bounds on the value of closed-loop control may be found by selecting the worst economics for the uncontrolled case.