Sooo many people on this app ask about this, so here's some basic info that can help.

1. Stress

Stress around your ovulation window can shift your period to a later date, or make you skip your period entirely. Stress in general will effect your period, if it occurs at any other time in the cycle it is less likely to effect you. Stress is an umbrella term, so any recent deaths, surgeries, stressing about your period, or anything else that makes you pull out your hair, can be included under here.

2. Illness

Similarly to stress, if you are sick around your ovulation window your period date might be shifted to a later date. However, there's not a lot of research on the connectivity between when your period starts and when you were sick, and how sick you had to be in order for it to have an effect.

3. Pills

If you change your dosage to previously used medication, or add a new daily pill to your body, your period can be delayed or even skipped. This is not strictly for prescribed medications; anything you add to your body can effect you.

4. Routine changes!

Many things fall under this, but the important thing to remember is even the smallest of changes in your daily schedule can effect you (i.e. getting up at a different time). Getting a new job is definitely something that might give you an "Oops, I'm late!" scare.

5. Exercise/Diet

If you change your exercise routine (by adding one to your life, getting rid of it, or becoming more hardcore) your period might hide from you for a while. Similarly, if you begin to eat a different kind of food, take out a certain food from your meals, or begin to cut back on a little of everything, blood may also cease to leak from your usual bleed-hole.

6.Weight Changes/Issues

On that note, if you suddenly loose/gain a bunch of weight, your body will need time to adjust. This includes exercising excessively! Also, if you are severely under/over weight, your period can cease for that month (or for much longer, if you're underweight)!

-This isn't bodyshaming. This is a scientific fact; if your diet is extremely unhealthy in either direction, your body will be effected. Usually not in a positive manner.

7. Vacations/Traveling

As much as you might hate to hear it, going to your dream location for a week or 5 may leave you worried the whole time. This one is more of a stress related issue (because who doesn't go to Disneyland worried about EVERYTHING?!??11!?!), but it's one of the biggest issues.

There are plenty, plenty more reasons. Some research will even tell you that the phases of the moon effect your monthly flow of pain and despair.

This website can provide further details: www.thefrisky.com/2013-03-25/dont-panic-7-reasons-your-period-might-be-late-besides-pregnancy/

Hope this helps at least one of you confused little ladies out there!