The legal background of the interest according to § 233a AO
In §233a AO, the interest on back tax claims and tax refunds is regulated. The principle of full interest applies, i.e. the interest relates to the period between the occurrence of the tax and its assessment (usually through the tax assessment). However, interest-only accrues after an interest-free waiting period of 15 months.
This means that only taxpayers whose tax is only set or changed for the first time after the waiting period has expired are affected by the full interest rate.
Judgment of the Federal Constitutional Court
The BVerfG sees in the interest of 0.5% monthly interest an unequal treatment of taxpayers whose tax is set after the waiting period has expired compared to those taxpayers whose tax is already set within the waiting period. The background to this is the contrast between the persistently low-interest rate and the 6% annual interest rate charged by the tax authorities.
The BVerfG still regards this unequal treatment for interest periods up to and including 2013 as constitutional. As of 2014, the interest on additional tax claims and tax refunds will be unconstitutional.
At the same time, the BVerfG declares the previous law to continue to be applicable for interest periods up to and including 2018. A continuation of the previous legal situation is only out of the question for later interest periods.
The legislature was also obliged to adopt a new regulation by July 31, 2022.