The Fourier spectral centroid formula for instantaneous frequency is extended to all times and to all analytic signals and is in a covenient computable form. Examples using two different synthetic even seismic wavelets show that the peaks and troughs of their instantaneous frequency may occur at the envelope maxima or minima, with possible singularities at the envelope minima. For a purely even or odd wavelet, either a turning point or a point of inflection occurs at the wavelet center of the instantaneous frequency and envelope. ¿ American Geophysical Union 1991