What is the chance of me being pregnant with a negative pregnancy test but i missed my period?

Tests are accurate: Today's home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A correctly done urine test will give a reliable result 3 weeks after sex (3 weeks after possible conception) or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon.