The contribution bases are found at the bottom of the payroll under the heading Determination of the S.S. contribution bases and joint collection and company contribution items.

There are three groups of contribution bases in a payroll:

Contribution base for common contingencies (BCCC): this contribution base is calculated by applying the following formula:

BCCC: Basic salary + salary supplements subject to contribution + the pro rata of the extra payments.

Although the worker receives the extra payments at the times stipulated in the collective agreement, this prorating is necessary as the Social Security will be paid month by month.

Contribution base for professional contingencies and joint collection: this is calculated by adding the BCCC + the value of the overtime worked. This is the contribution base used to calculate the percentage of the base for accidents at work, unemployment, vocational training and the Wage Guarantee Fund (FOGASA).

Base subject to personal income tax withholding: to calculate this contribution base, the total amount earned is taken and the amounts exempt from personal income tax, such as allowances, indemnities or products belonging to flexible remuneration plans, are subtracted.