Is this true??? Please help

Nakia
I seen online that your period is post to start 14-16 days after your ovulation date right ?? If so I had my last period on July 16 I ovulated on July 31st and when I did the count today is when I post to start my period but other places saying the 18 and on glow I'm late and on my other two I'm late I just  don't know when I should test???