Techniques for calibrating digitally controlled oscillators (DCOs) are disclosed. In an aspect of the disclosure, an initial set of control codes for operating the DCO is determined. A range of output frequencies produced from the initial set is identified. Gaps or instances of overlap are identified in the frequency range. For the overlap case, control codes are removed from the initial set that correspond to the overlap instance to establish a revised set. For the gap case, control codes are added to the initial set for producing frequencies values that fill the gap. An apparatus for performing the same is also disclosed.