Techniques are presented to improve the accuracy of and reduce the time required for calibration of an in-phase/quadrature (I/Q) transmission circuit. A measurement receiver measures the I/Q mismatch, where an RF phase shift is introduced to distinguish between the transmitter and measurement receiver I/Q mismatches. Rather than assuming an amount of introduced phase shift, a measurement is used to estimate the phase shift. This phase estimate is then used to determine and correct the I/Q mismatch in the transmitter and measurement receiver. An iterative process can be used to improve the I/Q correction factors. Using simple signal processing to measure the phase shift during calibration and to perform the image calibration calculations, the phase shifter requirements can be significantly relaxed, resulting in faster design time and reduced design area/cost. This approach results in reduced calibration time, thus contributing to reduced factory production time and enabling faster live mode image calibration.