# What is a normal cycle length? > Spoiler: there is a wide, healthy range. Category: Cycle basics · 4 min read · Written by the Splash team · Sources checked October 2026 URL: https://splash.care/learn/cycle-basics/normal-cycle-length ## Quick answer A normal menstrual cycle is 21 to 35 days long, counted from the first day of one period to the day before the next (NHS). Only about 13% of cycles are exactly 28 days. Varying by a few days each month is normal; regularly shorter than 21 or longer than 35 days is worth mentioning to a GP. - Normal cycle length: 21 to 35 days (NHS). FIGO allows 24 to 38. The average is around 28 to 29. - Periods usually last 2 to 7 days. - Small month-to-month changes are normal, especially in your teens and as you near menopause. - Your own pattern over several cycles is the best guide. ## Key facts - Normal range: 21 to 35 days (NHS). - Average cycle length was about 29 days across 600,000+ cycles, and only around 13% were exactly 28 days (Bull et al., 2019). - Gynaecologists’ FIGO system calls cycles under 24 days “frequent” and over 38 days “infrequent”. If your cycle is not 28 days, welcome to the majority. The NHS says a cycle typically comes around every 28 days, but anything from **21 to 35 days** is normal. Your period itself lasts **2 to 7 days**, usually about 5. **29.3 days** average cycle length in a study of 612,613 cycles from app users, with a spread of about 5 days either side. ## Different experts, slightly different lines There is no single magic number. The NHS and WHO use 21 to 35 days. The international gynaecology federation (FIGO) uses a slightly wider 24 to 38 days, and says the gap between your shortest and longest cycle should be up to about 7 to 9 days, with periods of up to 8 days. For teenagers, the American College of Obstetricians and Gynecologists says 21 to 45 days is normal. Either way, the picture is the same: a wide healthy range. ## What counts as a regular cycle? Regular does not mean identical. A few days of wobble from month to month is normal. It is the overall pattern over several cycles that matters, which is why [logging](https://splash.care/learn/cycle-basics/tracking-101) a few months is so helpful. ## What changes cycle length? - **Age:** cycles tend to be longer and less predictable in the first few years after periods start. In the app study, average [cycle length](https://splash.care/learn/glossary/cycle-length) got a little shorter with age in adulthood, then changes again in [perimenopause](https://splash.care/learn/glossary/perimenopause). - **Hormonal contraception:** pills, implants, injections and hormonal coils change bleeding patterns, and what looks like a period may be a [withdrawal bleed](https://splash.care/learn/glossary/withdrawal-bleed). - **Life:** [stress](https://splash.care/learn/cycle-basics/stress-travel-illness), illness, travel, [sleep](https://splash.care/learn/movement-sleep/sleep-cycle), and big changes in eating, weight or [exercise](https://splash.care/learn/period-care/exercise-on-period). - **After pregnancy or while breastfeeding.** **Myth:** A 32-day cycle means something is wrong. **Fact:** The NHS gives 21 to 35 days as the normal range, so 32 days is well inside it. What matters more is whether your cycle is steady for you and how you feel. > **Splash says:** check your Insights after three cycles. Your own average is far more useful than any textbook number. ### When to see a doctor See a GP if your cycles are regularly shorter than 21 days or longer than 35 days, your usual pattern changes, your periods last more than 7 days, you bleed between periods, or you have missed 3 periods in a row (and a pregnancy test is negative). ## Questions people ask ### Is a 35-day cycle normal? Yes. The NHS gives 21 to 35 days as the normal range. What matters more is whether your cycle is usually about the same length for you. ### How do I work out my cycle length? Count from day 1 of one period (the first day of proper bleeding) to the day before the next period starts. Averaging three to six cycles gives a better picture than one. ## Sources 1. [NHS: Periods](https://www.nhs.uk/conditions/periods/) 2. [Munro et al. (2018) The two FIGO systems for normal and abnormal uterine bleeding, Int J Gynaecol Obstet](https://pubmed.ncbi.nlm.nih.gov/30198563/) 3. [ACOG: Your first period](https://www.acog.org/womens-health/faqs/your-first-period) 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/) 5. [Jean Hailes for Women's Health: Periods](https://www.jeanhailes.org.au/health-topics/periods/) 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).