late period!!!

Hey everyone! So I use this app to mainly track periods. Well I was all peeped for it to come and nothing I'm officially 4 days late. Didn't stress it until yesterday . Took test and it was negative, took it 2 days late. I did see when I ovulated last and should have been around 7th of Jan. Which i did the deed same day. When should I test again and how likely do u think it will be positive?