Interactive Inbreeding Coefficient (F) Calculator
Estimate offspring inbreeding coefficient using Wright’s path method:
F = Σ[(1/2)(n1+n2+1) × (1 + FA)]
Each row below should represent one unique path through a common ancestor. Add separate rows for separate shared ancestors or independent loops.
What is an inbreeding coefficient?
The inbreeding coefficient (usually written as F) is the probability that an individual receives two identical copies of a gene from the same ancestral source (identical by descent). In practical terms, it quantifies how genetically related an individual’s parents are.
A higher F means a higher chance of homozygosity from shared ancestry. In population genetics, animal breeding, and conservation biology, this number helps evaluate genetic diversity and potential risk.
How this calculator works
Wright’s path method
This calculator sums contributions from each independent ancestral path:
- n1: generations from parent 1 to the common ancestor
- n2: generations from parent 2 to the common ancestor
- FA: inbreeding coefficient of that common ancestor (use 0 if unknown/non-inbred)
Contribution per path is (1/2)n1+n2+1 × (1 + FA). Total F is the sum of all valid path contributions you enter.
Example: first cousins
First cousins share two grandparents. If those grandparents are not inbred, each grandparent contributes (1/2)5 = 1/32, for a total of 1/16 = 0.0625 (6.25%).
Interpreting your result
- F = 0: no inbreeding detected from entered pedigree paths.
- 0 to 0.01: very low inbreeding signal.
- 0.01 to 0.0625: low to moderate, depending on species and context.
- ≥ 0.0625: often considered substantial in many breeding contexts.
Interpretation depends on the organism, trait architecture, effective population size, and management goals. In livestock or conservation programs, professionals often pair F with genomic metrics.
Best practices for accurate calculations
1) Avoid double-counting paths
The biggest source of error is entering the same loop more than once. Each row should be one independent path contribution.
2) Use reliable pedigree depth
Shallow pedigrees can underestimate true relatedness. If deeper ancestry is unknown, treat results as minimum estimates.
3) Include ancestor inbreeding where known
If common ancestors are themselves inbred, entering FA improves accuracy.
Important note
This tool is educational and provides deterministic pedigree-based estimates. It does not replace veterinary, medical, or genetic counseling advice. For high-stakes breeding or health decisions, consult a qualified geneticist and consider genomic testing alongside pedigree analysis.