Roll up number of appointments this calendar year

I have a requirement to roll up on account, the number of appointments this calendar year. This should automatically updated in the 01/01/2017 and automatically be zero.

I have created a roll up field to count the number of appointments but cannot use a filter to specify this year.

I've looks at the appointment to see if I can create a calculated two-option field to specify this year but again can't run the necessary calculation on the date field.

What options are open to me? I'd rather not use plugins/workflows as I think I'll have issues when the appointment is closed.