Under the VAT invoicing requirements, an invoice must contain a sequential number with one or more series of numbers, assigned uniquely by the invoice issuer to identify the invoice. According to the VAT Application Decree (Umsatzsteueranwendungserlass), an unbroken sequence of issued invoice numbers is not strictly required; however, gaps in the invoice sequence can in practice arouse the suspicion of the tax authorities. It may give rise to the suspicion that transactions were not properly recorded and therefore not included in taxable income.
In a 2023 ruling, the BFH addressed the question of the extent to which the tax office may obtain an estimation authority in the event of gaps in invoice numbering. According to the BFH, there is no automatic right to estimate in such cases. In the specific case, additional factual indications must exist suggesting that the taxpayer's information regarding taxable income is incorrect or incomplete. Considered in isolation, gaps in invoice numbering are not sufficient to justify an estimate.