Detachment folds seem conceptually and geometrically the simplest of all fault-related folds, and researches on them mainly focuses on geometric analysis and genesis mechanisms. Detachment folds are defined by competent rocks units and are cored by incompetent units deformed internally above a detachment horizon.Many detachment folds may analyzed using a simple geometric model. Early mathematical triangle’s models of detachment fold were developed into various geometric models, and the theoretical calculation of the excess area of these fold models is only related to the length and dipping angle of the fold limbs. However, in practical applications, the area-depth-strain (ADS) methods is widely used to calculate the depth to detachment, shortening, and parallel strain of the formation, indicating a disconnect between theoretical models and practical applications. Based on this, this article establishes a theoretical relationship between the excess area of concentrated special types of detachment folds, such as box fold,lift-off fold,symmetric fold and asymmetric fold, and the depth to detachment. Based on the definition of excess area and depth to detachment in the deformation of detachment folds, assuming a constant thickness of the stratum and known height of the fold core structure (Crestal Structural Relief) and strata dip angles of the fold-limbs, this paper establishes the mathematical relationship between excess area and depth to detachment of different structural geometric styles of Swiss Jura detachment folds, such as box shaped detachment folds, lift-off detachment folds, symmetrical detachment folds with limbs dip angles, and asymmetrical detachment folds with limbs dip angles. A fast calculation method for the shortening of detachment fold deformation and depth to detachment is obtained. It should be noted that according to the principles of geometry, the geometric shape of box-shaped detachment folds remains basically unchanged, while the geometric shape of lift-off detachment folds transform upwards into chevron folds. Symmetric folds and asymmetric folds, due to the presence of a basal incompetent plastic layers, have different mathematical relationships between their excess area and the depth to detachment above and below specific fold deformation layer. It is referred to as a transition layer or Detachment Conversion Layer(DCL). In addition to differences in geometric styles, the deformation mechanisms of this transition layer also differs.