ABSTRACT Observations of ω Centauri have been used to characterize the charge‐transfer efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. A set of formulae has been developed to correct aperture photometry for CTE loss with dependencies on the X‐ and Y‐positions, the background counts, the brightness of the star, and the time of the observation. The observations indicate that for very faint stars on a very faint background, the CTE loss from the top to the bottom of a chip has increased from about 3% shortly after the cooldown of WFPC2 (1994 April 23) to roughly 40% in 1999 February. In general, typical WFPC2 exposures are much longer than these short‐calibration images, resulting in higher background which significantly reduces the CTE loss and minimizes the CTE problem for most science exposures.