Ovulation Calculator

Health & Body

Ovulation day and fertile window from cycle length

Quick Answer

Ovulation Calculator: Ovulation day and fertile window from cycle length. Ovulation day ≈ next period − 14 days.

Last period start

Cycle length (days)

Next ovulation day

Sat, Aug 15

Fertile window: Mon, Aug 10 — Sun, Aug 16

Best conception window

Wed, Aug 12 — Sat, Aug 15

Next period expected

Sat, Aug 29

Next 3 cycles

Cycle	Ovulation	Fertile window
#1 ←	Sat, Aug 15	Mon, Aug 10 — Sun, Aug 16
#2	Sat, Sep 12	Mon, Sep 7 — Sun, Sep 13
#3	Sat, Oct 10	Mon, Oct 5 — Sun, Oct 11

How it works

Ovulation	Next period − 14 days (luteal phase is ~fixed at 14d)
Fertile window	Ovulation −5d to +1d (sperm live 5d, egg 24h)
Best window	3 days before through ovulation day
Accuracy	Calendar method ~76% — combine with LH strips or basal temperature

💡 Cycles vary month to month — the calendar method assumes regularity. If cycles differ by >7 days, ovulation prediction is unreliable; track basal body temperature or use LH test strips for precision. This is not contraception advice.

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How to Use

Enter body metrics: fill height, weight, age etc. as prompted by the 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

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: Ovulation day and fertile window from cycle length.
Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Ovulation estimate

Ovulation day ≈ next period − 14 days

Fertile window: 5 days before through 1 day after ovulation

FAQ

How do I use the Ovulation Calculator?

Open the page and fill in the input fields — results update automatically. Ovulation day and fertile window from cycle length.

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. Ovulation Calculator[EB/OL]. https://www.yijiansuan.com/en/c/health/ovulation

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