Even in the case of spouses an individual account is solely attributed to the account holder, in contrast to a joint account.
If one spouse transfers assets of his individual account or share deposit account to the individual account or share deposit account of the other spouse without consideration, the spouse liable to tax has to prove that no gift exists, e.g. the transferring spouse was trustee or fiduciary.
In practice, attention has to be paid since transfers of assets between spouses are not tax exempt according to the German Inheritance and Gift Tax Act. Furthermore, receipts of payments on a joint account may be considered half a gift if the other spouse regularly transfers funds to his individual account.
Especially in cases in which gifts between spouses exceeded the personal tax allowances of EUR 500,000, an equalization of accrued gains is advisable, as then the tax expires retroactively. For more details see Koeniger, The German Inheritance and Gift Tax, 2017, p. 321.