Cycle phase calculator: what phase of my cycle am I in?
Estimate today's menstrual cycle phase from the start of your last period and your usual cycle length, with how each phase tends to feel and how to move.
Runs entirely in your browser. Nothing you enter is sent anywhere.
An estimate, not a method
This tool helps you understand how you might feel. It is not for contraception or for planning or avoiding a pregnancy, and it cannot tell you when you ovulate. Real cycles vary, so treat every date here as approximate.
This tool gives general wellness information, not medical advice. If something feels wrong, talk to your doctor or midwife.
Quick take: Enter the first day of your last period and your usual cycle length, and the calculator estimates today's cycle day and phase: menstrual, follicular, ovulatory or luteal. It also shows how that phase commonly feels and when your next period may start. It is an estimate, not a contraception or fertility tool.
How it works
How does the cycle phase calculator work?
Most periods last between 2 and 7 days, usually about 5, and many cycles fall somewhere between 21 and 35 days.[3] That is why the calculator starts at 28 and 5 days, but you can change both.
A 28-day cycle is far from universal. In an analysis of more than 600,000 cycles, the average length was 29.3 days. The first half of the cycle averaged 16.9 days and the second half 12.4 days, and both varied a lot from cycle to cycle.[1] So the 14 days the calculator uses is a textbook figure, not a measurement of your cycle. Because the first half varies most, the calculator moves mid-cycle later in a longer cycle and earlier in a shorter one.
Can this calculator tell me when I ovulate?
The researchers behind the 600,000-cycle analysis noted that cycle length alone is not enough to identify fertile days, and that body signs such as temperature would need to be tracked as well.[1] Eggsports does not offer fertility or contraception tools. If you are trying to conceive or to avoid a pregnancy, a doctor, nurse or family planning service can talk you through reliable options.
What if my cycle is irregular or my period is late?
These limits come from the International Federation of Gynecology and Obstetrics.[2] If your usual length is shorter than 24 days or longer than 38, the calculator says so, because it is worth mentioning to your doctor, especially if it is new.
A late period has many possible reasons, including stress, sudden weight loss, a lot of exercise, some types of hormonal contraception, breastfeeding, perimenopause and pregnancy. If you have missed three periods in a row and you are not pregnant, see your doctor.[4] For the same reason, the calculator asks for a more recent date if the one you enter is more than three months ago.
Should I train differently in each phase?
The review recommended a personal approach, based on how each person responds across her own cycle.[5] Some patterns are common, though. Gentle exercise such as yoga, swimming, walking or cycling can ease period pain.[6] In the days before a period, many people notice tiredness, bloating, tender breasts or mood changes, and regular exercise is one of the self-help steps the NHS suggests for premenstrual symptoms.[7]
| Phase | What is happening | How it often feels | Movement ideas |
|---|---|---|---|
| Menstrual | Your period; hormones are at their lowest | Tired, crampy or inward for some, fine for others | Walking, yoga, swimming, easy cycling, or rest |
| Follicular | Estrogen rises after your period | Energy and mood often lift | Try something new or build strength |
| Ovulatory | Mid-cycle, around when ovulation tends to happen | Some feel at their most energetic | A harder session, if you feel strong |
| Luteal | Progesterone rises, then hormones fall | Steady at first, often more tired before a period | Steady sessions early, gentler options later |
If you want to turn today's phase, sleep and mood into a single movement suggestion, try the energy calculator. Wearing a heart rate variability tracker? The HRV rest-or-move tool explains why readings often dip in the second half of the cycle.
Frequently asked questions
What counts as day 1 of my cycle?
Day 1 is the first day of real bleeding, not the spotting that sometimes comes before it. Count from that day, even if your period started in the evening.
I don't know my usual cycle length. What should I enter?
Leave it at 28 days, a common starting point, and tick that your cycle varies if you are unsure. Noting the start date of your next few periods will give you your own average within a few months.
Does the calculator work in perimenopause or while breastfeeding?
It can, but cycles are often less predictable at these times, so the estimate is rougher. Tick that your cycle varies to see your next period as a range, and treat the phase as a loose guide.
Is my date saved anywhere?
No. The calculation happens in your browser, and nothing you enter is sent to a server, stored or put in the page address. Refreshing the page clears it.
Why does my phase feel different from the description?
The descriptions are what many people notice, not rules. Your sleep, stress, health and the length of your own cycle all change how a phase feels, so your experience is the better guide.
Sources
- Bull JR, Rowland SP, Scherwitzl EB, Scherwitzl R, Danielsson KG, Harper J (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine. doi:10.1038/s41746-019-0152-7
- Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee (2018). The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. International Journal of Gynecology & Obstetrics. doi:10.1002/ijgo.12666
- NHS (2023). Periods. nhs.uk. www.nhs.uk/conditions/periods/
- NHS (2026). Stopped or missed periods. nhs.uk. www.nhs.uk/conditions/stopped-or-missed-periods/
- McNulty KL, Elliott-Sale KJ, Dolan E, Swinton PA, Ansdell P, Goodall S, Thomas K, Hicks KM (2020). The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis. Sports Medicine. doi:10.1007/s40279-020-01319-3
- NHS (2026). Period pain. nhs.uk. www.nhs.uk/conditions/period-pain/
- NHS (2024). PMS (premenstrual syndrome). nhs.uk. www.nhs.uk/conditions/pre-menstrual-syndrome/