# What actually is a menstrual cycle?

> It is not just your period. It is a whole monthly loop.

Category: Cycle basics · 4 min read · Written by the Splash team · Sources checked October 2026
URL: https://splash.care/learn/cycle-basics/what-is-a-cycle

## Quick answer

- A cycle runs from day 1 of one period to the day before the next. The period is just the bleeding part.
- Your brain, ovaries and womb work together through hormones.
- Cycle length varies a lot between people. 28 days is an average, not a rule.
- A usual period lasts 2 to 7 days and loses about 20 to 90 ml of blood.

Your period is the bit everyone talks about, but it is really just the opening scene. A [Menstrual cycle](https://splash.care/learn/glossary/menstrual-cycle) is the full loop your body runs, from the **first day of one period to the day before the next one starts**.

## Who is in the cast?

- Your **brain** (the hypothalamus and pituitary gland) sends [hormone](https://splash.care/learn/cycle-basics/hormones-explained) messages.
- Your **ovaries** grow and release an egg, and make [Oestrogen](https://splash.care/learn/glossary/oestrogen) and [Progesterone](https://splash.care/learn/glossary/progesterone).
- Your **uterus** (womb) builds a cosy lining, the [Endometrium](https://splash.care/learn/glossary/endometrium), in case an egg is fertilised.

Every cycle, these three talk to each other in a feedback loop. Rising oestrogen thickens the womb lining and prompts an egg to be released. After that, progesterone helps the lining get ready. If no [pregnancy](https://splash.care/learn/fertility-ttc/early-pregnancy-signs) happens, both hormones fall, the lining comes away, and that is your period. Then the loop starts again.

## Period or cycle?

These two words get mixed up all the time. Your **period** is the bleeding. Your **cycle** is the whole loop, bleeding included. The NHS says a period lasts 2 to 7 days (usually about 5), is heaviest in the first 2 days, and loses about 20 to 90 ml of blood in total, which is roughly 1 to 5 tablespoons.

## How to count your cycle

1. Day 1 is the first day of real period flow. [Spotting](https://splash.care/learn/glossary/spotting) just before it is usually not counted (apps and clinics differ a little, so pick one rule and stick to it).
2. Keep counting every day until the day before your [next period](https://splash.care/tools/period-calculator) starts.
3. That total is your [cycle length](https://splash.care/learn/glossary/cycle-length). [Logging](https://splash.care/learn/cycle-basics/tracking-101) in Splash does the maths for you.

**13%** of cycles were exactly 28 days in a study of 612,613 cycles from app users. "Textbook" is far from the norm.

**Myth:** Everyone has a 28-day cycle and ovulates on day 14.

**Fact:** In that same study the average cycle was 29.3 days, and only about 1 in 8 cycles were exactly 28 days. Ovulation day varies from person to person and from month to month. (The study only counted cycles where ovulation could be detected, in people who chose to use an app, so treat it as a good guide rather than a final answer.)

**Myth:** Your period and your cycle are the same thing.

**Fact:** The period is the bleeding part. The cycle runs from day 1 of one period to the day before the next, so it is much longer.

> **Splash says:** you will have roughly 480 periods between ages 12 and 52 (fewer if you have pregnancies, according to the NHS). Getting to know yours early is time well spent.

**Quick quiz:** Which day is "day 1" of your cycle?

1. The day you ovulate
2. The first day of full bleeding
3. The last day of your period

Answer: The first day of full bleeding. Day 1 is the first day of proper period flow. Everything else in the cycle is counted from there.

## Sources

1. [NHS: Periods](https://www.nhs.uk/conditions/periods/)
2. [NHS: Periods and fertility in the menstrual cycle](https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/)
3. [Cleveland Clinic: Menstrual cycle](https://my.clevelandclinic.org/health/articles/10132-menstrual-cycle)
4. [Bull et al. (2019) Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles, npj Digital Medicine](https://pmc.ncbi.nlm.nih.gov/articles/PMC6710244/)

This is general information, not medical advice. Splash can’t diagnose. If you’re worried, talk to a GP, pharmacist or sexual health clinic. In an emergency call 999 (UK) or 911 (US).