Sorry if this has been asked elsewhere - I didn't find it if so.

Both my husband and I got letters from the city of Zurich asking us to confirm some things about our employment for tax rate purposes. Mine was easy, since I don't work. For my husband, the letter asked for his "monthly wage." What should we put here - he gets paid on the 13 month schedule.
- Yearly salary / 12?
- Yearly salary / 13?
- Should it include other benefits? (e.g., he gets a transportation subsidy)

Thanks!

Total/everything paid in 1 year divided by 12.