Calibrated option bounds The arbitrage-free interval gives bounds for the reasonable prices of a contingent claim in an incomplete market. In the approach of Ritchken and Kuo these bounds are computed numerically by solving two optimization problems over martingale measures for a discrete market model. It turns out that this approach is very sensitive to the choise of the model, and there is no general rule for choosing the right one. This paper shows how the available market information can be used to overcome this difficulty. Our approach is close to recently developed calibration approaches where the market information is used to pin down a particular pricing model that is consistent with observed security prices. An advantage of the present approach is that it relies less on user specified information and thus avoids problems with possible miss-specifications. Numerical tests on S&P500 options demonstrate the accuracy and robustnes of the method.