A dynamic comparator with background offset calibration is provided. The dynamic comparator includes at least one input differential pair, a first back-to-back inverter, a second back-to-back inverter, and an integrator. The input differential pair includes two current branches, wherein one of the current branches has an input referred offset. The first back-to-back inverter determines which one of the two current branches has the input referred offset in response to a first clock signal and generates two control signals accordingly. The integrator generates two calibration voltages for the input differential pair in response to the two control signals, so as to calibrate the input referred offset. The second back-to-back inverter determines a difference between two input signals received by the input differential pair after the input referred offset is calibrated in response to a second clock signal and outputs two comparison signals accordingly.