buy a preg test, it's a whole $10. From there you can decide what to do (aside from start using protection regularly)
You can't really quote very good odds for each individual times. When you quote failure rates with birth control its quoted in pregnancies per year. The worst i think is the rythm method which is around 50%. That means half the women get pregnant per year based on this system. Not using protection isn't safe and you are more likely than not to get pregnant.
What ive realized is that the more a person worrys about getting pregnant they will but if they are chill about it they seem to never get pregnant. Thats just my observation.
Not as high as 50%, no. _even_ if an egg got fertilized the odds of it implanting and starting to divide successfully aren't great. BUT, there's definitely a significant chance, so you want to act fast. One option is an emergency contraceptive pill, Plan B. http://www.go2planb.com/ForConsumers/Index.aspx Best bet is to contact a doctor/pharmacy for advice. It's effective, but you need to take it ASAP--within 72 hours (3 days) of unprotected sex, and the sooner the better.