First Response can detect the pregnancy hormone as early as 6 days sooner than the day of your missed period (5 days before day of expected period). The amount of pregnancy hormone increases as pregnancy progresses. The \"day of your missed period\" means the day after your period is due. The First Response Kit can be used 6 days before the day of your missed period. The First Response kit is over 99% accurate when used on the day of your missed period, your due date and the day prior to your due date. The Kit is 62% acccurate when used 6 days before the day of your missed period.