This paper presents an approach for depth estimation of a buried sphere from numerical fourth-horizontal derivative anomalies obtained from total field magnetic data using filters of successive window lengths (graticule spacings). The method involves using a parametric relationship between the depth and a combination of windowed observations at four symmetric points around the origin of the source. The problem of depth determination from fourth-derivative total magnetic anomalies has been transformed into finding a solution to a non-linear equation of the form f (z) = 0. The present method can be applied to observed data even when the regional magnetic field is represented by a fourth-order polynomial. Finally, the validity of the method is tested on different synthetic examples with and without random errors and tested on a field example from Senegal, West Africa.