How do you calculate the incubation period of cp i saw my friend on mon and then again on thur and she had shingles is't from last day or the for firs?

7 to 21 days: Most of us have already had varicella (chicken pox) or been immunized, so we are immune. "Last day or first" is not an issue. If you were in the same room, especially face- to -face, for over 15 minutes you may have sustained significant exposure. If your friend was treated (acyclovir, famcyclovir, valacyclovir) your risk is very low. If your friend was already 2 or 3 weeks into it your risk is l