My Bloom BuddyHow long is my cycle?
Enter the dates your last few periods started and we'll work out your average cycle length, how much it varies, and whether it sits in the typical range. It all runs in your browser: nothing is stored or sent.
How to count a cycle
A cycle is counted from the first day of one period to the first day of the next — not from the day your period ends. Day 1 is the first day of real bleeding, not spotting.
So if your last period started on the 3rd and the one before it started on the 6th of the previous month, you count the days between those two start dates. That number is your cycle length.
Two dates give you one cycle. Three or four give you an average, which is far more useful — almost nobody has the same length every single month.
What counts as a normal cycle length
For adults, anywhere between 24 and 38 days is considered typical. The famous 28 days is an average pulled from a population, not a standard anyone is failing to meet. A 25-day cycle and a 36-day cycle are both entirely normal, and neither is better than the other.
Two stretches of life are naturally less regular: the first year or two after your first period, when cycles are often long and unpredictable while things settle, and the years approaching menopause, when they frequently shorten, lengthen, and skip. Irregularity in those windows is usually the body doing exactly what it is supposed to.
Why your own number matters more than the average
Every period prediction is built on your cycle length. If an app assumes 28 days and your real average is 33, it will tell you your period is late every single month — five days of unnecessary worry, on repeat. Replace the assumption with your own number and everything downstream gets more accurate.
It also gives you a baseline. “Is this normal?” is a hard question in the abstract, but an easy one once you know your own pattern. A 31-day cycle means nothing on its own; a 31-day cycle when you have run 26 days for two years means something worth noticing.
Common ways people miscount
- Counting from the day your period ends. Always count from the first day of bleeding.
- Counting the days you bleed. That is your period length, a different number.
- Starting from spotting. Day 1 is the first day of proper flow.
- Using one month. A single cycle is a data point; three or four is a pattern.
When to check in with someone qualified
- Cycles consistently shorter than 21 days or longer than 45
- Three or more missed periods in a row
- A lasting change from your own usual pattern
- Bleeding that is unusually heavy, or comes with severe pain or large clots
This is a calculation from the dates you entered, for gentle awareness only. It is not medical advice and not a form of birth control. Anything that concerns you is worth a conversation with a doctor or nurse.
Common questions
How do I work out my menstrual cycle length?
Count from the first day of one period to the first day of the next. That number is your cycle length. It is not the number of days you bleed, and it is not counted from the day your period ends — those are the two most common mistakes.
What is a normal cycle length?
Anywhere from 24 to 38 days is considered typical for adults. The often-quoted 28 days is an average, not a target — a 26-day cycle and a 34-day cycle are both perfectly normal. In the first year or two after your first period, and in the years approaching menopause, cycles are commonly longer and less predictable.
Is it normal for my cycle length to change every month?
Yes. Very few people have the same length every month. A variation of a few days either way is ordinary, and stress, illness, travel, disrupted sleep, and changes in training or weight can all shift a cycle. Consistently large swings — or a lasting change from your own usual pattern — are worth raising with a doctor or nurse.
How many periods do I need to track to get an accurate cycle length?
Two period start dates give you one cycle length. Three or four give you an average, which is much more useful, because it shows both your typical length and how much you vary. Six months of dates gives a genuinely reliable picture.
Why does my cycle length matter?
It is the number every period prediction is built on. Using 28 days when your real average is 33 will push every estimate five days early and make your period feel permanently late. Knowing your own number makes everything else more accurate.
Got your number? Use it to work out when your next period is due, or read more in the Cycle Library.
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