After how many years exactly do we get the same calendar as the current year? When can I safely reuse my calendar again for the present year?
According to this link http://www.timeanddate.com/calendar/repeating.html - there is no definitive answer (2016's calendar matches every +/-28 years for some time, where 2015's does not match years as periodically (+6,+6, +11, ...).
On a further note: due to the calculation of holidays (e.g. Easter is the first Sunday after the first full moon in Spring [ https://en.wikipedia.org/wiki/Easter#Computations ] ) holidays will not easily repeat periodically either.