Relevant Costing assigns future costs and revenues to the
decision being made. It includes only those cash flows which will
be affected by the decision.
Relevant cost must be future (incremental) cash flows affected
by the decision and therefore ignore the following:
- Sunk Cost: Those costs which have already been
incurred before the decision is made. For example - if a company
already purchased material then the cost of the material at that
time is irrelevant. Instead the current replacement value (if
material is still regularly used) or the scrap value (if material
is no longer used) would be considered the relevant cost to the
decision.
- Unavoidable Cost (committed cost): Those costs
which will be incurred / cannot be avoided regardless of the
decision. The difference between these and the sunk cost is the
time at which the costs are incurred. These are future cost whereas
sunk cost is in the past. For example – Expenses like Depreciation,
property tax, lease payment, interest expense already incurred
before the decision and any difference will be treated
accordingly.
- Apportioned Costs: Those costs which have been
split between units of production or service based on some
arbitrary allocation method, For example – fixed machine service
cost apportioned based on the number of machine hours used.
However Relevant cost do include Opportunity cost; of the
benefits foregone when the decision being made means that
alternative opportunity must be rejected. For example: If a company
owns a asset which can be leased out to other companies, but is
used on short term internal contract instead, them the relevant
cost would include the external rental income foregone.