Don't worry that is a safe day to have sex. If your periods are regular than use this ovulation calendar at www.ladytimer.com and it will tell you when it's safe to have sex and when it's not safe.
Actually there are NO safe days to have sex. We don't know when she ovulates, if her cycles are regular, what her cycles days are, how long her period is, etc. I know people who ovulate as early as CD 8-10. Sperm can survive for up to 5 days in the female body, 7 days in perfect conditions. Unless you're trying to get pregnant you NEVER have unprotected sex for any reason.
We also have an ovulation tracker - http://www.medhelp.org/user_trackers/gallery/ovulation We
also have an iPhone and Android app that will allow you to do this - http://www.medhelp.org/land/my-cycles
If you have an android phone, you can search for it in the app market.