The fixed costs or fixed costs (only in Spain) are those costs that are not sensitive to small changes in the activity levels of a company, but rather remain unchanged in the face of these changes. The antithesis of fixed costs is variable costs.

The differentiation between fixed cost and variable cost is essential to obtain information suitable for making decisions based on costs.

Fixed costs are usually related to the productive structure and that is why they are also usually called structure costs and used in the preparation of reports on the degree of use of that structure.

In general, fixed costs accrue periodically: once a year, once a month, once a day, etc. That is why they are also often called periodic costs.

Example of fixed costs, if a company produces 100 units of chickens, and its fixed cost of renting the premises is $1000, the rent will be the fixed cost, since even if it produces more chickens in a month, the rental cost will remain within that margin.

Sunk or fixed costs (in Mexico). Saying that the condition for producing requires that the price be equal to or greater than the average variable cost is equivalent to stating that the company that incurs losses will only be compensated for producing if these are equal to or less than the fixed costs. This analysis leads us to the concept of fixed or unrecoverable cost, or sunk cost, that is, one that has already been committed and cannot be recovered. It is a cost that belongs to the past. Given that nothing can be done with sunk costs, in the face of the decisions that the businessman makes about whether to produce or not, the most appropriate thing is to ignore them. The analysis presented shows that, when faced with the decision to produce or close, sunk costs are irrelevant. It is assumed that these types of costs cannot be recovered by temporarily stopping production. In this sense, the company's fixed costs are irrecoverable in the short term and, therefore, can be ignored when deciding the quantity of production.

According to R. JAcobi, fixed costs are those costs that the company must pay regardless of its level of operation, that is, whether it produces or does not produce, it must pay them. A fixed cost is an expense that the company must incur, even when the company operates at half speed, or not at all, which is why they are so important in the financial structure of any company. This is the case, for example, of payments such as the lease, since even if nothing is sold, it must be paid. It also happens with almost all labor payments, public services, insurance, etc.