Period & Ovulation Calculator

Cycle prediction, ovulation day and fertile window

Quick Answer

Period & Ovulation Calculator: Cycle prediction, ovulation day and fertile window. Period & Ovulation Calculator uses standard health formulas to compute accurate results instantly.

Last period start

Cycle (days)

Duration (days)

Today: cycle day

Menstruation · next period 9/6

Ovulation day8/23

Fertile window8/18~8/24

Best conception8/20~8/23

PMS likely8/30~9/6

Next 3 cycles

#	Period	Ovulation	Fertile window
1	9/6 ~ 9/10	8/23	8/18 ~ 8/24
2	10/4 ~ 10/8	9/20	9/15 ~ 9/21
3	11/1 ~ 11/5	10/18	10/13 ~ 10/19

Cycle phases reference

Menstruation (d1-5)

Low energy, iron loss

Follicular (d6-13)

Rising estrogen, best for training

Ovulation (~d14)

Peak fertility, BBT rises 0.3-0.5°C

Luteal (d15-28)

PMS may appear in late phase

💡 Calendar method assumes a fixed 14-day luteal phase — accuracy ~76% for contraception; cycles vary ±7 days in most women. For contraception rely on contraceptives, not the calendar. See a doctor if cycles regularly fall outside 21-35 days or vary >7-9 days month to month.

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How to Use

Enter body metrics: fill height, weight, age etc. as prompted by the Period & Ovulation Calculator.
Read value and grade: results appear instantly with an authority-based classification.
Check reference tables: confirm your range and healthy targets against the tables on this page.
Back-solve your goal: adjust inputs to see what it takes to reach a target.

Key Points

Period & Ovulation Calculator is a free online health tool — open and use, no sign-up.
All calculations run locally in your browser; your data never leaves the device.
Key capability: Cycle prediction, ovulation day and fertile window.
Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Period & Ovulation Calculator formula

Period & Ovulation Calculator uses standard health formulas to compute accurate results instantly.

FAQ

How do I use the Period & Ovulation Calculator?

Open the page and fill in the input fields — results update automatically. Cycle prediction, ovulation day and fertile window.

Are the results accurate?

Results follow published international standards (WHO, ACE, IOM) and are for reference only.

Can this replace medical advice?

No. Always consult a qualified healthcare professional for health decisions.

Is it free? Do I need to sign up?

Completely free. No registration, login or download required.

Does it work on mobile?

Yes. The responsive design works on all devices.

Related Guides

Source & Updates

Based on WHO, ACE, IOM and other published international standards. Last updated: 2025-07

Authoritative sources:

Last updated: 2026-08-04

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Cite this page: YiJianSuan. Period & Ovulation Calculator[EB/OL]. https://www.yijiansuan.com/en/c/health/period

Results provided by this tool are for reference only and do not constitute professional advice.