In an RC calibration circuit, a single reference current is used to generate voltages across both a resistive and capacitive element. The component value of one of the resistive and capacitive element is successively altered until the voltages are substantially equal. Additionally, parasitic capacitances in the circuit are precharged to the resistive element voltage prior to the comparison. The RC calibration circuit eliminates the errors due to current matching and parasitic capacitances in prior art calibration circuits. The circuit includes a comparator and a digital control circuit (DCW) including a successive approximation register (SAR) holding the value of the digital control word used to control the component value of the tunable resistive or capacitive element. The SAR alters the DCW in an iterative, bit-by-bit binary searching pattern in response to the comparator output.