If you have a 4-day delay in your period and a negative test result after 3 days, it could be due to a variety of reasons. Sometimes, menstrual cycles can be irregular even for people who are usually very regular. It is not necessarily a cause for concern. Additionally, pregnancy tests can sometimes give false negative results, especially if taken too early. Some companies guarantee 99% accuracy if the test is taken 7 days after a missed period. It is recommended to wait a week and if your period still hasn't arrived, you can take another pregnancy test as a precautionary measure.