How accurate is a HPT 6 days after the missed period?

I'm also curious about something: if you ovulate later than usual (like say 2 days later than normal), does it push back the date of your period? Or is the date of your next period JUST based on the date of your last period + cycle length? Thanks :-)|||I was always told 95% depending on which brand you used and how sensitive the test was..some dont pick up until 50 mIU/mL others 25 mIU/mL|||99.9 % accurate|||I think they are pretty accurate at that point!!! Good luck!