Which of the following is not included in a cost calculation?

In the context of cost calculations, external income sources are not included because they do not represent an expense or cost to the entity calculating the costs. Rather, external income refers to potential revenues or funds that come from outside the primary operations of the business. This could include returns from investments, grants, or income from other ventures, which do not directly affect the cost of producing goods or services.

On the other hand, the base price, tax amount, and shipping fees are all essential components of cost calculations. The base price represents the fundamental cost of acquiring a product or service. The tax amount is typically an obligatory charge added to the base price, affecting the total expenditure. Shipping fees are relevant as well, reflecting the costs incurred to transport goods to their final destination. All these elements contribute directly to understanding the comprehensive costs involved in a transaction, while external income sources pertain more to revenue generation rather than cost assessment.