If my cycle came on december 19 2015 is my correct ovulation date 1/6/16 ..

Cycle length: If you had a 27 day cycle you would ovulate on 1/6/16, if the first day of your last menstrual period had been 12/19/15 (27 - 14 = 13; 12/19 + 12 = 12/31 + 1 = Jan 1). In a fertile cycle the second half of the cycle has to be 14 days.

Can't tell from that: If one has a 28 day cycle, ovulation happens around day 14. If one has a 30 day cycle, it happens around day 16. That is because ovulation takes places about 14 days before the estimated first day of the NEXT period. So, to figure this out, you have to guess the first day of the NEXT period (even if that period never came, due to getting pregnant) and then look backwards 2 weeks on the calendar.