Could i be pregnant

Patient: I was last on my period starting the 26.12.11 and me and my boyfriend had unprotected sexthrough to the 4th January when he returned to work. I have a very regular 27 day cycle and i am due on again on the 21.01.12. on the ovulation calculators it states that my fertile period is from the 6th- 11 th January. what are the chances i could be pregnant?Thanks