Worked example
Last period on Thursday, October 1, 2026, a 28-day cycle and a 5-day period. On Saturday, October 10, you are on cycle day 10: in the follicular phase.
Ovulation is estimated on October 14 (ovulation phase October 13 to 16), the luteal phase runs from October 17 to 28 and the next period is expected around October 29.
How it is calculated
- Count the days since the first day of your last period: that first day is day 1.
- Estimate ovulation on day cycle length − 14.
- Menstrual phase during your period, follicular until 2 days before ovulation, ovulation phase from the day before ovulation to 2 days after, then luteal until your next period.
The 4 cycle phases at a glance
| Phase | Days (28-day cycle) | What is happening | Common feelings |
|---|---|---|---|
| Menstrual | 1 to 5 | Hormones are at their lowest and the uterine lining is shed. | Tiredness, cramps, need for calm. |
| Follicular | 6 to 12 | Estrogen rises while a follicle matures in the ovary. | Energy and motivation coming back. |
| Ovulation | 13 to 16 | LH surge, the egg is released (around day 14). | High energy, confidence, often a higher sex drive. |
| Luteal | 17 to 28 | Progesterone dominates, then hormones drop before the period. | Calmer, then sometimes irritability, tender breasts, cravings (PMS). |
How the calculator finds your phase
It uses the same rules as the Luteal app. Ovulation is estimated at cycle length − 14. The menstrual phase lasts as long as your period; the follicular phase runs until 2 days before ovulation; the ovulation phase covers the day before ovulation to 2 days after; the luteal phase runs until your next period.
If the expected period date has passed, the calculator does not start a new cycle at random: it treats you as still being at the end of the luteal phase, with a late period.
Energy and mood: tendencies, not rules
Changes in estrogen and progesterone affect energy, sleep, appetite and mood in many people, but not in everyone, and not in the same way. The descriptions here are common tendencies: your own experience matters more.
The best way to learn your rhythm is to log your mood and energy alongside your periods for a few months: patterns often show up after 2 to 3 cycles.
When your symptoms are worth talking about
- Intense sadness, anxiety or irritability that disrupts your life every month before your period: this may be premenstrual dysphoric disorder (PMDD), which can be treated.
- Period pain that stops you working or studying despite usual painkillers.
- Very irregular cycles, no period for more than 3 months, bleeding between periods.
- If you have thoughts of self-harm, do not wait: contact your local emergency number or a crisis line (988 in the US, 116 123 Samaritans in the UK).