Depends. Have you had unprotected sex since your last period? If not, then it's likely late due to stress, illness or something like that
Stress can be a big factor to delay a period. I've been here myself. The more you panic and stress about the what ifs of being pregnant then more likely it is to be late or even miss a period. I wouldn't worry untill you are at least a week or 2 late. You may of even just ovulated abit later this month. Try not to worry.