20 Days for the first 5 years you are with the company. After 5 years 26 days.
Split is 12 winter and 8 summer days. Sundays are not counted in so in reality you have. 13 and 9 days.
Off days can be added before or after your vacation days.
This year i had 17 days for winter 13 days for summer time.
If you ask them to add your days off before or after your vacation, than you have to suck it up for the rest of the month and fly with minimum rest between duties.
Turkish airlines is not good when it comes down to vacation days. Don't expect 42 Days off vacation like in the middle east carriers.