An empirical model based on a harmonic analysis approach for calculating the peak density of ionospheric F layer over Chungli (24.95° N, 121.23° E) for all levels of solar activity is proposed. The harmonic coefficients were obtained by normalizing the NmF2 data collected during the period 1976 to 1983 to a common level of solar activity. The coefficients exhibit expected seasonal variations. A set of 49 coefficients comprising the mean, first, second and third harmonics was found to be sufficient to recreate monthly mean NmF2 under any level of solar activity. The proposed model requires only the precalculated set of coefficients as input and enables one to use the NmF2 values so calculated as single station input to IRI or other similar models.