The goal of this contribution was to develop a reliable quality indicator reflecting the potential success of differential carrier phase ambiguity resolution for kinematic Global Positioning System (GPS). The indicator must be operable without any communication link between the rover and the reference station. Two common existing GPS quality measures are combined: firstly, the SIGMA model, which is a signal intensity-based weighing scheme reflecting the actual signal quality, and secondly, the ambiguity dilution of preci- sion (ADOP), which is an indicator of the geometric strength of a constellation. Together, these two established indicators form the newly developed ADOP+. In the first part of the present work, a calibration is conducted in order to obtain the parameters for the SIGMA model. In the second part, the ADOP+ is derived and implemented. A practical test is per- formed on a motorcycle in order to validate the concept. The ADOP+ is proven to be meaningful and well performing within the empirical case. It is able to predict the success of phase ambiguity resolution in the majority of situations.