Hello Toytown members, I hope that some will be able to answer my following questions. First, some background information for you to understand my situation: I did tax returns every year from 2012 and until 2016 with a particular tax number 148/XXX/XXXXX I got married in Jan 2017 and changed my tax class to 3 My wife started working as a freelancer in 2019 and we received two letters ( or tax numbers 146/XXX/XXXXX ) from Finanz Amt one for both of us and second only for my wife's freelance activity. Now, I want to do a tax return for the years 2017 and 2018 (voluntarily) and for 2019 (mandatory). It would be great if you can answer the following questions: Which tax number should I use for 2017 & 2018? The old one (148/XXX/XXXXX) or new one that is assigned to both of us (146/XXX/XXXXX)? Also, My wife used the new joint tax number (146/XXX/XXXXX) on bills from 2019 do we need to rewrite the bills? I think she should have used the new tax number only assigned to her. Thankyou!