Which documents are relevant?
In 2017 the law changed, which is almost equivalent to a revolution in tax law. It was already announced in July 2016 that you must not submit supporting documentation with your tax return (Steuererklärung) as of 01/01/2017. From that point on, you are only required to to retain all your documentation that applies. This states that supporting documentation only needs to be submitted after an expressed written request. The aim is to keep the public official's workload as light as possible.
Attention: Nevertheless, all supporting documentation should be kept until the tax assessment (Steuerbescheid) is final and thus, rejection is no longer possible.
However, this law only applies as of 2017. This means that some supporting documentation is necessary for 2016.
Compulsory (Belegpflicht) until 2016
There are still expenses in the tax return, which the original supporting documentation must be attached and submitted.
Capital gains tax and interest deductions (Kapitalertragsteuer und Zinsabschläge)
Related tax certificates (Steuerbescheinigungen) must be proven. Banks usually send corresponding supporting documentation automatically.
Exceptional charges (außergewöhnliche Belastungen)
If an event occurs that forces someone to spend too much, then according to the law, the one that is "burdened" applies. Such expenses may only be incurred for the taxpayer or for a relative. The exceptional charges include, e.g. medical expenses, maintenance costs and much more (e.g. Krankheitskosten, Unterhaltskosten etc.).
Relatives are dependent. That means your mother will pay you financially, you for her, your grandma for you, and so on. In such cases, these payments must be stated in the tax return and proven accordingly.
Retirement provision (Renten)
Contributions to Riester pensions or Rürup pensions must also be proven. As a rule, insurance companies automatically send you the necessary documents.
Social benefits (Sozialleistungen
What many do not realize is that benefits have to be proven as well. You will receive supporting documentation from the respective authority from which you received benefits. Hartz IV does not have to be stated in the income tax declaration, because it is a purely social benefit.
Donations are voluntary. It is particularly important that no consideration is expected. To be of additional value as a donor, donations may only be made to non-profit organizations (in the form of money, volunteer work, etc.). Only donations to non-profit organizations based in Germany are included in the tax return. It is important that the donation recipient also issues receipts that the tax office recognizes.
Anyone who does not use the disability lump sum (Behindertenpauschale), but instead, submits much higher expenses, must be able to provide supporting documentation for this. By the way, pension offices issue severely handicapped ID cards (Behindertenausweis) and declarations, which can then be forwarded to the tax office (Finanzamt).
Certificate of study (Immatrikulationsbescheinigung)
If, for example, a loss carryforward (Verlustvortrag) is submitted, the enrollment fee must also be attached. The form confirms that you are enrolled at university to study.
Capital-forming benefits (vermögenswirksame Leistungen)
Certificates of capital-forming benefits are issued annually by investment institutions, banks or building societies.