Ahnentafel numbers are used in many genealogical ancestry reports (as opposed to descendancy reports) to describe the relationship of an ancestor to a base person, whose Anhentafel number is 1 (one). While pedigree diagrams show the same relationship in a much more pleasing fashion by using "wiring" lines from child to parent, they have two major limitations. First, pedigree diagrams become very unwieldy after a few generations -- when they need to be continued on other pages or screens. Secondly, due to limited space they report only basic details for an individual -- desirable in-line individual data, like notes, discussions, and sources, are almost always omitted in a pedigree diagram.

The larger ancestral reports use a book-type format with the generations acting as chapters. The individuals are related by their unique Ahnentafel number, rather than by a wiring diagram.

Ahnentafel numbers are simple and elegant. All are whole numbers greater than zero (positive integers). The base person, the individual whose ancestry is being reported, is assigned Ahnentafel number 1. For any person in the ancestry (including the base person) whose Anhentafel number is N, the father is assigned Ahnentafel number 2N (2 times N) and the mother gets number 2N + 1. There are several useful rules that derive from this scheme. Like: any female ancestor has an odd number. And N's husband has number N - 1. Ahnentafel numbers are described in detail elsewhere. For a start see Leon Chrisman's discussion. Or you may want to just search for Ahnentafel number using one of the Web's search engines.

This Ahnentafel calculator was born of the need to rapidly determine a person's exact ancestry from an Ahnentafel number. Ahnentafel numbers, while they convey the same information as pedigree wiring diagrams, lack their glitz entirely. This calculator is a small attempt to bridge the gap between utility and glitz. The calculator is limited to 51 generations, including that of the base person (#1) -- about 2.25 quadrillion ancestors. [ 2.25 peta-ancestors? ] More than 1000 years' worth. The largest Ahnentafel number accepted by the calculator is 2,251,799,813,685,247 (2^51 - 1). Enjoy!