Ancestor Generation Calculator
Calculate the total number of ancestors at a specific generation, cumulative ancestors, or the relationship between two people based on generational distance.
Mode
Generation 0 = yourself, 1 = parents, 2 = grandparents, etc.
Use 2 for standard biological ancestry.
Results will appear here.
Formulas Used
- Ancestors at Generation N: A(N) = pN, where p = number of parents (typically 2)
- Cumulative Ancestors (Gen 1 to N): Σ pi = p(pN − 1) / (p − 1) for p ≠ 1
- Coefficient of Relationship: r = (1/2)a + b, where a and b are each person's generational distance to their closest common ancestor
- Cousin Degree: Degree = min(a, b) − 1; Removal = |a − b|
- Approximate Shared DNA: cM ≈ r × 6,800 cM (total human genome length)
Assumptions & References
- Standard biological ancestry assumes exactly 2 parents per person (p = 2).
- The coefficient of relationship formula r = (1/2)a+b assumes no inbreeding and autosomal (non-sex-linked) inheritance.
- Pedigree collapse (shared ancestors appearing multiple times) is not modeled — theoretical counts become unrealistic beyond ~30 generations.
- The total human genome is approximately 6,800 cM; shared DNA estimates are statistical averages and vary in practice.
- Generation labels follow genealogical convention: Generation 0 = proband (you), Generation 1 = parents, Generation 2 = grandparents, etc.
- References: Wright, S. (1922). "Coefficients of Inbreeding and Relationship." American Naturalist. | ISOGG Wiki: Coefficient of Relationship.