Drop your payslips as PDF or XPS (a year’s worth, or whatever you have). Each one is checked against the rules of ITS year: the contributions Order and, from 2022, the Tax Agency’s withholding algorithm. If you add the Social Security contribution base report, it is matched month by month with what your payslips say.
It can be downloaded for free from the Social Security e-office (Import@ss → “Informe de bases de cotización”), with Cl@ve or a text message. It says which base your employer declared each month, which is what counts for your unemployment benefit and your pension. If it does not match the payslip, ask your employer: it is what nobody checks.
Your employer computes your withholding with what it EXPECTS to pay you in the year and the data in your form 145. If your salary or situation changes, it adjusts it mid-year, and you can also ask to be withheld more. That is why a difference is a warning, not an error. What is not withheld now is paid in the tax return.
The PDF and XPS files are read in this browser. They are not uploaded anywhere, not stored and not put in any link: when you close the tab, they are gone.
They are read in this browser: nothing is uploaded anywhere or stored.
General Social Security scheme, employees. Contributions: 2013 to 2026. Income tax: 2022 to 2026 in the common tax territory (not the Basque Country or Navarre, which have their own tables; nor Ceuta, Melilla or the La Palma deduction).