Really. I'm smart. Or at least mostly smart! I used a few different online ovulation calculators. The dates they gave me are all way different. Any idea why that might be? One site (web md) says February 13th to the 17th. Another one (countdown to pregnancy) says February 10th to the 14th And a third one (babycenter) says February 11th to the 16th. I suppose the smartest/safest thing would be to use the whole range (the 10th through the 17th) as the fertile period, but why the discrepancy?