The Federal Law on withholding tax will change on January 1st 2021. The cantons will be directly impacted.

The Geneva Cantonal Tax Administration gave a videoconference to the FER on April 23, 2020 to announce and explain what will change locally next year.

If you were unable to attend, you can download the slides below  . 

One new thing (among others ) :

When someone has several jobs and you need to take into account the total rate of occupation of all jobs for the calculation of the withholding tax, indicate this rate in tab 5 of the employee management, tab "Withholding Tax/Taxes":