The Fabry-Perot interferometer (FP) is modeled as a transparent medium between two absorbing coatings with finite thickness, typically two metallic films. The absorption in the first coating causes the reflectance of the FP to differ from an Airy function. The maxima and minima of the reflected fringes are displaced from those of the transmitted fringes, and the reflected maxima and minima are asymmetrical. We derive expressions that quantitatively explain previous experimental results. interferometer, reflectance, absorptance.