Hi Worried Guy 01. The dates of the tests are regularly checked and it is illegal to sell out of date stock. The most recent tests to have been dispatched to Amazon expire in 2021. The chance of the test result changing is not due to the accuracy of the test however is down to the individuals immune system. For example at 4 weeks 50% of people would have antibodies to HIV, at 6 weeks this increases to 95% and at 12 weeks this is 99.9%. I would recommend re-testing at 12 weeks to get a conclusive result and put your mind at ease. I hope this helps and thank you for choosing BioSure. Kindest regards Francesca Bard, BioSure (UK) Ltd