irregular periods😂😂😭

So according to <a href="">Eve</a> and the data from my last period, my period is 3 days late. However, my period is always late, or sometimes a little early because I have irregular periods. If your suppose to take a pregnancy test if your period is late, how will you know when to buy a pregnancy test when you ha e irregular periods anyway? I'm sorry if this is a stupid question, still new to the whole tracking thing