take a test?

im on 3 different ovulation apps and each one says I'm supposed to start my period on August 27-30 I haven't started yet. and I'm getting anxious and nervous to know if I'm finally pregnant or not. when should I take a test to know when the results are right or not. Not sure which calculation is right on my period and I don't want it to be to early and get discouraged if it negative or too early to tell