When should I test?

Natasha

So my period is due on the 27th July (3 days time) however I ovulated late this month on the 17th/18th July on CD 23 ish. so my question is shall I test when I miss my period on Saturday/ Sunday or should I wait until 14dpo based on the 17th/18th of the month assuming my period is that late. What does eveyone think?