Can you help me calculate when i'm ovulating? january from 18-22nd. february period on 16-19. march 13-16th. my periods are not always regular.

9-12: Ovulation occurs typically 9 to 12 days following start of menstrual cycle. Your periods actually seem pretty regular to me. You can also consider trying to use an ovulation predictor kit. They are fairly inexpensive. Also measuring first thing in the morning, you basal body temp. This is a good predictor if done the same every day, first thing in the morning. Write it down and look for spike.

Cycle length - 14: Your cycle length is from the first day of one to the first day of the next period. Your cycle length jan-feb was 29 days (jan 18 to feb 16). Your cycle length feb-mar was 25 days. Subtract 14 days from your cycle length to find your likely ovulation date. For jan-feb cycle: 29-14 = day 15 (feb 1st); for feb-mar cycle: 25-14 = day 11 (feb 26th) ovulation. (day 1 is the first day of your period).