A system for determining a correction for an output value of a time-to-digital converter within a phase-locked loop is provided. The output value relates to a time difference between an input signal and a reference signal supplied to the time-to-digital converter. The system includes a digitally-controlled oscillator configured to generate a first signal independently from the output signal. The first signal has a first frequency different from an integer multiple of a reference frequency of the reference signal. The system further includes a frequency divider configured to generate the input signal for the time-to-digital converter based on the first signal. The input signal has a second frequency being a fraction of the first frequency. Further, the system includes a processing unit configured to calculate the correction using a distribution of output values of multiple time differences.