Hello
I appreciate your query
What you want to know is the safe period method ( Rhythm method )
Normallly, in a 28 day cycle, day 14 is day of ovulation
For 5 days before and after that, you are at risk of
pregnancy if
unprotected intercourse occurs
That is , Day 10 - Day 20 of your menstrual cycle ( if day 1 is first day of bleeding ) are unsafe day
and rest are safe days
for eg in current cycle, if 7th
Dec is first day of bleeding, then 17th - 27th december are unsafe days.
Please understand that this method is extremely unreliable, and has more than 25 % failure rate
Because days of ovulation vary in each female in each cycle
maybe Day 12 or as late as Day 19, even if your periods are regular
So , relying on this calculation alone is risky
Condoms of various types are available in the market, which facilitate
safe sex and prevent infections too
Many safe, new low dose pills too are available with minimum of side effects.
Please consider these too
take care.