After the end of the calendar year, you can submit an application for a tax refund at your Tax Office. This income tax declaration is used to ascertain whether you have paid too much income tax. If this is the case, then the overage will be refunded to you.
You must provide documentation of special expenditures or extraordinary liabilities. This is why you should keep receipts for work materials (i.e., computers, storage media), receipts for business travel costs and public transportation tickets (insofar as these were not paid for by your employer), costs for private pension insurance, expenses for business-related moves (also from abroad), etc., organize these documents by year, and submit them together with your tax return to the Tax Office.
Because German tax regulations are complex and all tax forms are exclusively in German, we recommend in many cases that you hire a tax advisor (for a fee), or that you seek support from an income tax assistance organization. You can also use software that takes you through the steps required to fill out a tax return.
Yes, you have to submit your tax forms latest by 31 July of the following year. If you engage the services of a tax consultant, the deadline is later.