Wright's Coefficient of Inbreeding is a decimal fraction (sometimes expressed as a percentage) representing the probability that a homozygous gene pair will be identical by descent from both sides of a pedigree. In the formula, FX is the COI, FA is the COI (if known) of the ancestor common to both sides of the pedigree. n1 and n2 are the numbers of generations on each side of the pedigree between the individual whose COI is being calculated and that ancestor. In dog pedigrees, the most practical method of calculating COI is by using computer software programmed for the purpose; COI calculation on paper is too extensive and laborious to be practical in most cases.