Old Calendar Bulgarian Orthodox Church

The Old Calendar Bulgarian Orthodox Church is an Old Calendarist church which follows the traditional Eastern Orthodox liturgical calendar, the Julian Calendar, and rejects ecumenism. From its creation in 1993 it was led by Metropolitan bishop Photius of Triaditsa.

In the teachings of the church, Ecumenism and Sergianism are identified as contemporary ecclesiological heresies that fundamentally corrupt the very concept of the Church. Ecumenism is described as a multi-stage, infiltrative heresy that seeks to reconstruct an "undivided Church" by uniting "divided Christians," yet it often avoids clear doctrinal expression, instead adopting a diplomatic stance that allows it to coalesce with "official Orthodoxy". Conversely, Sergianism is rooted in the delusion that deception and collaboration with enemies of the Church—originally atheist regimes—could serve to protect Her. The core ecclesiological distortion of Sergianism lies in its redefinition of "canonicity," which is stripped of its spiritual truth and transformed into a formal managerial technique used to demand absolute subordination to the episcopate, regardless of whether that leadership upholds the Truth. In its modern form, often termed neo-Sergianism, this manifests as a pathological servility to secular authorities for mercenary motives or social status, ultimately contributing to the rise of "official Orthodoxy," which is viewed as a diluted, pluralistic surrogate for authentic Orthodox.

Bulgarian Old Calendarists face difficulties from the Bulgarian authorities, who refuse to recognize them as an official religious entity.