Differential cost :

It may be defined as “the increase or decrease in total cost or the
change in specific elements of cost that result from any variation in operations”. It
represents an increase or decrease in total cost resulting out of :
(a) producing or distributing a few more or few less of the products;
(b) a change in the method of production or of distribution;
(c) an addition or deletion of a product or a territory; and
(d) selection of an additional sales channel.
Differential cost, thus includes fixed and semi-variable expenses. It is the difference
between the total costs of two alternatives. It is an adhoc cost determined for the purpose
of choosing between competing alternatives, each with its own combination of income and
costs.