For the most reliable results, you want to wait 19 days after the sex in question. If you were expecting a natural period, your fertile time starts about 19 days before your period, so testing when your period is late comes out to about the same as 19 days after sex. But since you're on the pill, if you had an ovulation it would be more random.
A withdrawal bleed is a good sign you're not pregnant, since the pregnancy hormones usually prevent you from bleeding even when it's a withdrawal bleed and not a natural period. But missing a withdrawal bleed doesn't for sure mean you're pregnant.
You can always take one test if you miss your bleed and then another 19 days after the sex you're concerned about.
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Date: 2011-03-05 05:52 pm (UTC)A withdrawal bleed is a good sign you're not pregnant, since the pregnancy hormones usually prevent you from bleeding even when it's a withdrawal bleed and not a natural period. But missing a withdrawal bleed doesn't for sure mean you're pregnant.
You can always take one test if you miss your bleed and then another 19 days after the sex you're concerned about.