Here is the calculator that takes into account working and non-working days. Enter the initial date, enter the number of working days - the calculator will show the next working day.
Note 1:You can input negative days, and the calculator will count backward.
Note 3: Since the transfer of holidays is regulated by the government's special decree, which usually comes in late October, calculator takes into account only the transfers for the 2008 - 2021 period.
Updates: Here is another calculator: Number of working days between two dates (for Russia)
Updates: 2021 is now supported