Period & Ovulation Calculator
Estimate your next period, ovulation day, fertile window, and current cycle phase. Customize for personal luteal phase length and PMS prediction.
The day bleeding started, not when it ended.
Forecast for the next 6 cycles
- Cycle 1in 28dPeriod29 Aug 2026 – 2 Sep 2026Ovulation15 Aug 2026
- Cycle 2in 56dPeriod26 Sep 2026 – 30 Sep 2026Ovulation12 Sep 2026
- Cycle 3in 84dPeriod24 Oct 2026 – 28 Oct 2026Ovulation10 Oct 2026
- Cycle 4in 112dPeriod21 Nov 2026 – 25 Nov 2026Ovulation7 Nov 2026
- Cycle 5in 140dPeriod19 Dec 2026 – 23 Dec 2026Ovulation5 Dec 2026
- Cycle 6in 168dPeriod16 Jan 2027 – 20 Jan 2027Ovulation2 Jan 2027
Related tools
How to use
- 1
Pick the date your last period started (the first day of bleeding, not the last).
- 2
Enter your average cycle length — count from one period start to the next.
- 3
Optional: your average period length and how many future cycles to forecast.
- 4
Customize lets you tune the luteal phase length (12-16 days — varies between people) and adds PMS window + current-phase tracker.
- 5
The result shows next period, fertile window, ovulation day, current cycle phase, and the PMS window when symptoms typically appear.
Frequently asked questions
For people with regular cycles (length varies by less than ~5 days between months), it's accurate to within 1-2 days. For irregular cycles, it's a rough guide only. Ovulation prediction kits (OPKs) measuring luteinizing hormone, or basal body temperature tracking, are more precise — but for most purposes a calendar estimate is enough.
The luteal phase is the time from ovulation to your next period. For most people it's stable at 14 days, but it varies 12-16 days between individuals (it's the FOLLICULAR phase that varies more between cycles). If you've tracked your ovulation with OPKs or basal body temperature and know your personal luteal phase length, set it in Customize for more accurate predictions.
By counting back from your next predicted period: ovulation = next period − luteal phase (default 14 days). So if your cycle is 28 days, ovulation is around day 14. If it's 32 days, ovulation is around day 18. This is more accurate than 'day 14 of every cycle' because the luteal phase is much more consistent than the follicular phase.
The ~6-day span when intercourse can result in pregnancy: 5 days before ovulation + the day of ovulation + 1 day after. Sperm live up to 5 days inside the body, but the egg only lasts 12-24 hours after release. The day of ovulation and the day before are the highest-chance days.
PMS (pre-menstrual symptoms) — bloating, cramps, mood changes, breast tenderness — typically appears 5-11 days before your period starts. The calculator shows a 7-day PMS window before the next period. Severity varies enormously between people and between months; some have very little, others have PMDD (premenstrual dysphoric disorder) and need medical care.
No. Calendar-based methods alone are not reliable contraception (typical-use failure rate is ~24% per year per the CDC). For pregnancy prevention, use a medical method (IUD, hormonal, barrier) — and consult a doctor about what suits you. This calculator is for awareness, family planning, or to figure out when your next period is due.
The day before ovulation and the day of ovulation. Pregnancy rates peak at around 30% per cycle when intercourse happens on those days. The fertile window starts wider (5 days before) because sperm survive — but the peak is the day before ovulation.
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Source: ACOG (American College of Obstetricians and Gynecologists) — standard luteal-phase model · Last verified 2026-06. ACOG. This tool provides estimates only and is not legal, tax or financial advice. Always verify your specific situation with the relevant UAE authority or a licensed advisor before taking action.