A numerically controlled oscillator includes a phase accumulator that outputs a phase word and a clock that periodically outputs a clock signal in accordance with a delay interval. The phase accumulator outputs a new phase word in response to receiving the clock signal. A clock controller calculates a timing drift and adjusts the delay interval to reduce the timing drift. A method includes receiving a plurality of frequency control words, calculating a delay interval, accumulating the frequency control words in accordance with the delay interval to generate a phase word, converting the phase word to a waveform, calculating a timing drift, and adjusting the delay interval to reduce the timing drift.