How many days can a girl be "late" before it's worry time?

[Yossarian]

My girlfriend is 3 days late today. She is on the pill and has been on it since November. What are the chances she's pregnant?

[jw]

keep a box of tests in your nightstand - no need to worry - ever.

[chilidog]

I wouldn't worry over 3 days; I'd worry if she were 10-15 days late. Did she change birth control pills in November, or just now started taking them in November?

[Fanny]

no days.
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[Yossarian]

She changed pills in November..