I recently became a resident of Germany on a student residence permit and will soon marry my partner, who is a German citizen. I still have a small US-based income (Army Reserves). What do I need to be aware of when filing taxes in the next year? Is it best to file as Married Filing Separately? How do we avoid any double-tax, for example, my income being taxed by both US and Germany?
Because you are a US Citizen/Resident, your worldwide income is subject to US Taxation. The good news is that while the US will tax your Army Reserve Income, they will also give you a credit for any foreign tax paid so you can avoid any "double taxation."
As for your Filing Status, you are Single unless you are married before December 31, 2022. If you do marry by then, you can treat your spouse as a resident alien for tax purposes (MFJ) or file MFS or HOH if you meet those requirements.
You may find the following IRS link helpful: See the General FAQs