We can't know an exact percentage on your chances for pregnancy, but anytime you have unprotected sex, you have an increased chance of pregnancy.
The more times you had unprotected sex, the higher your chances of pregnancy.
We know this is a stressful time for you, and you may talk with other women in the Am I Pregnant discussion Group. I hope you find the information below helpful while you determine the cause of your missed/late period, or to help you understand your chances of pregnancy after having unprotected sex (or after a birth control failure).
Late or Missed Period
A normal range for a cycle is 21-35 days ("day 1" is counted as the first day of your period), and many women expect their period to begin on an exact calendar date each month (say, the 15th of each month). Women's cycles, even the most "regular" 28-day among us, cannot use the calendar date as the primary clue that our period is "late", as it is simple math: a "perfect" 28-day cycle that occurs on the 15th one month will occur on the 12th of the next month (in a 30-day month) or on the 11th (in a 31-day month).
Since your period has not begun when you expected it to, please know there are many reasons a woman's period may be "late". Of course, pregnancy is a possibility, but so are other factors: excessive stress, dramatic fluctuation in weight, recent illness, new medication, medical condition or just an "unknown" fluctuation that can happen without cause. The normal fluctuations can occur as our bodies reacting and interacting to the environment around us, and our periods can become irregular for a few cycles, almost "unexpectedly", and this can be perfectly normal. If you are worried about an irregular period or symptoms that have changed, please review the information: How to Know if Your Period is Normal.
Low Chance of Pregnancy Because It was Not My Time to Ovulate....Right?