Thanks for sharing your health question with the EmpowHER community!
A period typically is on a 28 day cycle. So, beginning the first day you begin your period, you will typically see it again 28 days later.
It's important to note periods lengths can range from cycle to cycle due to factors like birth control, stress, travel, medication, weight loss and more.
If you started your last period on September 29, your next period would start October 27, give and take a few days. If your period doesn't start within 3-4 days of the 27th, I recommend taking a pregnancy test if that is a concern.
I hope this helped! Let me know if I can help with anything else.