The earliest you can get a positive result on the most sensitive pregnancy tests is 3-4 days after implantation.

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Implantation needs to occur before hCG is produced, and implantation generally happens between 6-12 days post ovulation, so the HPT would be positive as early as 9 days, and on average 13-14 days, after ovulation/fertilization.

For this reason, it makes sense to wait until 10-12 days after ovulation. However, even 10-12 days after ovulation, over one-half of pregnant women will still show a negative result.
If you did not have an hCG injection (common in fertility treatment, brands include Profasi, Pregnyl and Novarel), you can believe the positive results, but a negative result does not necessarily exclude a pregnancy. If your period is late, test again.

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Your hCG levels should rise at least 60% every 2 days and many people won't have a positive HPT until the first day of a missed period or even a few days later.