A method and apparatus for determining an RC (resistive-capacitive) time constant is disclosed. In one embodiment, a method comprises determining a first period of oscillation when an oscillator is operating in a first configuration. The method further comprises determining a second period of oscillation when the oscillator is operating in a second configuration. A measurement circuit is configured to determine a resistive-capacitive (RC) time constant of the oscillator by determining a mean of the first and second periods.