Charging the same gross salary and receiving less money in the account is possible. One of the explanations is the withholding of the IRPF: if the percentage deducted on the payroll increases, the take-home pay decreases even if the company has not reduced the salary.
December often draws attention because it coincides with the end-of-year closing and, in many cases, with an extra payment. However, the regularization is not an exclusive measure of that month, nor is it necessarily applied to all workers.
Why withholding may change at the end of the year
The IRPF Regulations include the review of the type when the compensation or certain circumstances used to calculate it change. It also includes the case of a person who continues working for the same employer after the period initially planned.
A pay increase, variable remuneration, or an extension of the contract can alter the annual forecast. The company must recalculate what should be withheld, taking into account the updated information and the amounts already deducted.
This does not allow concluding that any decline in bank income is correct. Before attributing it to the IRPF, you have to check whether the hours worked, the allowances, the contributions, or other items on the payslip have changed.
An example to understand the adjustment
Let’s suppose, only as an example, that the annual amount to be withheld after a review was 3,000 euros. If 2,600 had already been deducted and 2,000 euros of remuneration subject to the adjustment remained, 400 euros would be missing to be withheld.
Dividing those 400 euros among the 2,000 pending amounts would produce a percentage of 20%.
The regularization takes into consideration what is missing to be withheld and the pending remunerations, with the limits and rules of the regulations. That is why a percentage applied at the end of the fiscal year can be different from the one used months earlier.
What to look at if December comes with less money
The comparison should be made between pay slips, not only between bank transactions. You need to review the total accrued, the base on which the IRPF is applied, the percentage, and the amount withheld.
If the gross salary stays the same, but the withholding increases, that difference can explain part or all of the drop in net pay. If other items have also changed, each one will have to be analyzed separately.
To request a useful explanation from the company, it is of interest to request the expected annual remuneration, the amount withheld up to that point, and the calculation that justifies the new rate. Asking only why the percentage has increased can leave the data that caused the change unclear.
How to check the calculation with the official tool
The Agencia Tributaria offers a [withholding calculation service. On the 2026 exercise page there are versions differentiated by date of application, so the one corresponding to the period you want to review must be chosen.
For the check to be meaningful, equivalent data to that used in payroll must be entered. Comparing a calculation that includes only the monthly salary with another that incorporates extra payments and variable remuneration can produce different results without identifying where the disagreement lies.
Saving the result and the data entered makes it easier to consult the human resources department. It also makes it possible to check whether the difference disappears when correcting an amount or a circumstance.
Model 145 is delivered to the company
Model 145 serves to communicate to the payer the data that affects withholdings and their changes. Lal Agencia Tributaria specifies that it is not submitted to it: it is received by the payer, who must keep it.
If the personal or family data used by the company no longer corresponds to the actual situation, the communication should be reviewed. The form does not allow choosing a lower percentage freely; it provides the information needed to calculate it.
What to ask before closing the last payroll
The review can be started before receiving the December payment. A specific message to the payroll department avoids having to reconstruct the calculation afterwards:
"I request to confirm the expected annual remuneration, the withholdings already made, and whether any pending regularization exists for the remaining payrolls, indicating the data used".
If the inquiry refers to an extra payment, it is advisable to identify its gross amount as well and the receipt in which it will be paid. To review the result, the previous payrolls, the model 145 communicated, and the company’s response must be kept.