
"Additive relationship" is a genetic term used to measure the fraction of "like genes" shared by two humans or animals. It suggests how reliable the records of one will be in predicting genetic matters for the other. Determining the additive relationship between any two individuals is a two step process:
 Determine the number of generations separating them, by using the mathematical process described under the Sequential System. The resulting number is expressed as n in the formula at the bullet below.
(Alternately, one may simply count the number of generations intervening between the two individuals  ascending from Person A to the common ancestor, C, and descending back down to Person B. Persons A and B, themselves, are not counted. C is counted in both the ascent and the descent. The total number of generations between A and B is the generational n.)
 Calculate the actual additive relationship by applying the formula (1/2)^{n}  meaning one divided by two, raised to the n th power.
To continue our example of Queen Elizabeth and King Harald, it is easy to see from table 2 that eleven generations separate them in the basic calculation. If this were their only kinship, then their additive relationship would be 0.00048828125  or, expressed more simply, they would be 0.049% related to each other. This table is arrived at through the following calculation: n = 5 + 6 = 11 (1/2)^{11} = 0.00048828125
In a complex kinship, the total additive relationship is calculated by adding together the individual additive relationships already determined for each KinCode element. Table 3 below lists the additive number for each relationship shown for Queen Elizabeth and King Harald and then calculates the total additive relationship  i.e. 0.05078125, which makes them 5.08% related to each other.

