The tax authorities must estimate the tax bases even when they cannot determine the reason for an incoming payment or the taxpayer is unable to provide sufficient details regarding this payment.

In the case of unknown incoming bank payments, the taxpayer is obliged to clarify to the tax authorities what the payment is for. If the reason for incoming payment cannot be determined the tax authorities are allowed to conclude that this income must be taxed.

The Munich Finance Court has decided that a supplementary estimate of the operating income is permitted in the case where the source or reason for the incoming payments are not indicated.