What day should i ovalate if my last period was on the sixth?

Depends: It depends on your normal cycle length. We tend to calculate timing based on an idealized cycle length of 28 days from start of one period to start of the next. Estimated ovulation day would be cycle day 14 or 12/19-20 in your case. If your cycle length is longer, ovulation will be later and vice versa. Home ovulation prediction kits are a good way to determine when you will ovulate.

Cycle minus 14 days: It's math! (agree with dr. K) how long are your cycles? Subtract 14 from your usual cycle length. 28 day cycle minus 14 is day 14. 30 day cycle minus 14 is day 16. There are free web and app calculators (look, ma, no math!) and also you can use home ovulation predictor kits that have charts to use. You just need to know the length of your cycle. Good luck!