Ancestor Count Calculator

Every generation back, the number of possible ancestor slots doubles -- 2 parents, 4 grandparents, 8 great-grandparents -- and Theoretical Ancestors sums that doubling series (2^1 + 2^2 + ... up to Generations Back), reaching over 4,000 by 11 generations and over 2 million by 20. Theoretical Ancestors depends only on Generations Back, not on Pedigree Collapse Rate or Known Ancestors -- it's purely the mathematical ceiling of how many ancestor slots exist, before accounting for the fact that real family trees don't fill every slot with a unique person. Adjusted (w/ Collapse) applies Pedigree Collapse Rate to bring that ceiling down toward reality: in populations where people commonly married relatives (small or geographically isolated communities), the same ancestor can occupy more than one slot in the tree, so the true number of distinct people is lower than the theoretical count. The discount is not a literal one-time percentage cut -- it compounds as (1 - Pedigree Collapse Rate/100) raised to the power of Generations Back divided by 3, so collapse accumulates more heavily the further back you look; treat Pedigree Collapse Rate as a dial controlling how aggressively the discount grows with depth, not as an exact "this percent of ancestors are duplicates" figure.

Tree Completeness then divides Known Ancestors by the adjusted count to show what fraction of your realistic ancestor pool you've actually identified, and Unknown Ancestors is simply what's left. Collapse Significance Gen is a fixed reference point (around generation 20), not a value computed from your specific inputs -- it marks roughly where theoretical ancestor counts start to exceed plausible historical population sizes for many regions, which is where pedigree collapse becomes statistically inevitable rather than merely possible. What this doesn't do: adjust generation length for your specific family (it treats "10 generations" as a fixed research window regardless of whether your ancestors tended to have children young or old), and it applies Pedigree Collapse Rate as a single uniform percentage rather than modeling which specific ancestors are the duplicated ones.