Calculating the Synchronization
Currently, 1 Thout in the Old Coptic Calendar corresponds to either 11 September or 12 September in the Gregorian Calendar. However, this was not always the case. Prior to the institution of the Gregorian Calendar in October 1582, 1 Thout used to correspond to 29 August.
The New Coptic Calendar proposes a one-time shift, either 13 days or 14 days (depending on whether the preceding year is a leap year in the Old Coptic Calendar) that sets 1 Thout in the New Coptic Calendar as 29 August in the Gregorian calendar.
For example, if the one-time shift were to take place in 2019, 1 Thout 1736 AM in the New Coptic Calendar would correspond to 29 August 2019 AD, as opposed to 12 September 2019 AD.