Well, I have used up a couple of packs recently even though I knew they couldn't be positive! However, when I tested for no reason last year and it was positive between then and the 10wk dating scan despite a blood test, an early scan then a viability scan at 6 weeks I used 21 tests - covered all brands and shop own makes. Since losing Evie at 34 weeks I've been stockpiling again as no matter what happens I know I'm going to need a lot of convincing!