When will the first period be missed after sex?

ok If there is one and a half weeks until my next period and I have sex, will fertilisation happen before that next period, causing me to miss it, or will I have to wait till the next month?

In other words, if I have that period one week and a half after sex does it mean that I am absolutely not pregnant?



Info: 21 years old, not on pill, wasn't planning on having sex, no protection. Periods are usually chaotic but last few month have been regular, and usually only last 3-4days.When will the first period be missed after sex?if you had normal period (not light! not short!) after some period after unprocted sex, it means you are not pregnant - discover more belowWhen will the first period be missed after sex?Fertilisation will occur before the period, causing you to miss it, but it is possible to still bleed at the time you would normally have a period, so the only sure way to know is to wait and take a testWhen will the first period be missed after sex?usually ovulation (and fertilization) occurs about 12-16 days after the START of the period, in the middle of the cycle, but every period may be different, and it is impossible to predict for certain

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PLEASE, USE PROTECTION EVERY TIMEWhen will the first period be missed after sex?
Fertilization happens within 3 days of having sex. So if you have a period a week or two after you had sex it is a 100% sure thing your not pregnant. This is why when you buy Plan B they tell you you must take it within 72 hours of intercourse as sperm can't survive inside of you for more than 72 hours.