Could I be pregnant if my period is twelve days late but have a negative home pregnancy test?

A negative home pregnancy test taken 12 days after a missed period is usually accurate. There are rare instances where levels of the pregnancy hormone hCG may be very low and not detectable by a home pregnancy test. To be sure, you should see a doctor for a blood test to accurately rule out pregnancy. The blood test can detect even very low levels of hCG and provide a definitive answer.