If my period started at 11:30 PM, does that count as the first day? Like day one, and the next day is day two?

If it was actual red blood, you can count that day as day 1, yes! But if it was just a very light brown spot that barely stained your underwear right before bed, many people prefer to mark the next day, when the real flow starts, as day 1.

Actually, Day 1 of the menstrual cycle is officially the first day you have actual bleeding (not just that light brown spotting). If you went to the bathroom at 11:30 PM and already saw real blood, that day on the calendar was your first day, and when midnight struck, it became day two. But if you only noticed it in the morning or prefer to count the next day because you were already going to sleep, it's perfectly fine. The important thing is to have an idea of when it started so you can track your cycle.

Most people bleed for 3 to 7 days, and the first period can be much shorter and lighter. Tell an adult if you need to change your pad every 1 or 2 hours, if your period lasts more than 7 days, if you pass clots larger than about 2.5 cm, if the blood leaks onto your clothes or bed, if you stop doing daily activities because of your period, or if you often feel tired or short of breath.

In the first year or two, it's normal for cycles to vary, more or less from 20 to 45 days from the start of one period to the start of the next, and a shorter or longer cycle than the previous one, on its own, is not a cause for concern. Stress can also delay your period. Tell an adult if, several times in a row, it's more than 45 days between periods, if you go 3 months without a period after it has started, or if, several times in a row, it comes with less than about 3 weeks in between.

To avoid racking your brain trying to remember what time it started or counting days on your fingers, you can mark everything in the Sosô app, which records the start and end of your period and shows your calendar very accurately.