If the first day of my last period was december 28th and when would i ovulate and when is the earliest time i could take a pregnancy test ?

After missing period: A urine pregnancy test done correctly will give a reliable result 3 weeks after sex (after possible conception) or 1 week after missing a period. The test can be done sooner, but there is no need to do that. Patience is a virtue. Being patient and waiting will avoid false negatives and avoid spending extra money to repeat tests.