Ovulation Calculator

Estimate ovulation date and fertile window from LMP and cycle length — see next 3 cycles predicted.

Ovulation Calculator

Estimate ovulation date and fertile window from LMP and cycle length — see next 3 cycles predicted.

Last menstrual period (LMP)

Cycle length (days)

Enter values above and click Calculate — results will appear here with the formula explained.

Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)

How does this work?

Ovulation is estimated as 14 days before next expected period (LMP + cycleLength -14). The fertile window spans a few days before and after due to egg and sperm survival.

This is a statistical estimate, not contraception. Cycle variability, stress and health affect timing — use with cervical mucus or LH kits for better accuracy, not medical advice.

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Disclaimer: Results are estimates for informational purposes only and do not constitute professional medical advice. Consult a qualified professional for decisions.

What is Ovulation?

Ovulation is estimated as 14 days before next expected period (LMP + cycleLength -14). The fertile window spans a few days before and after due to egg and sperm survival. Formula: Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)

Quick Answer

Ovulation Calculator: Estimate ovulation date and fertile window from LMP and cycle length — see next 3 cycles predicted. Formula: Ovulation = LMP + cycleLength - 14 days. Example: With LMP 2026-01-01 and 28-day cycle, ovulation around 2026-01-15, fertile window about Jan 12-17, next period Jan 29.

What it does: Estimate ovulation date and fertile window from LMP and cycle length — see next 3 cycles predicted.
Formula: Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)
Inputs: Last menstrual period (LMP) · Cycle length (days)
Example: With LMP 2026-01-01 and 28-day cycle, ovulation around 2026-01-15, fertile window about Jan 12-17, next period Jan 29.

Calculator Inputs at a Glance

Field	What to enter
Last menstrual period (LMP)	Enter a value
Cycle length (days)	e.g. 28

All fields use the exact formulas shown below — results include step-by-step breakdowns you can verify by hand.

How to Use This Calculator

1Enter LMP and usual cycle length in days.
2Calculate to see estimated ovulation, fertile window and next period.
3Track 3+ cycles to refine personal average — single-cycle estimates vary.

Formula Used

Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)

Ovulation is estimated as 14 days before next expected period (LMP + cycleLength -14). The fertile window spans a few days before and after due to egg and sperm survival.

This is a statistical estimate, not contraception. Cycle variability, stress and health affect timing — use with cervical mucus or LH kits for better accuracy, not medical advice.

AdSense ready — add NEXT_PUBLIC_GOOGLE_ADSENSE_PUBLISHER_ID

728×90 — AdSense

Worked Example

With LMP 2026-01-01 and 28-day cycle, ovulation around 2026-01-15, fertile window about Jan 12-17, next period Jan 29.

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Frequently Asked Questions

QIs fertile window 6 days?

Commonly about 5 days before ovulation plus ovulation day, due to sperm living up to 5 days. This tool shows ovulation ±3 days as a simple window.

QCan this prevent pregnancy?

No, it is not contraception. Fertility awareness for contraception requires daily tracking and training.

QWhat about irregular cycles?

Use average of last 3 cycles for length, but expect wider fertile uncertainty — consult a clinician for guidance.

Quick Answer

What it does: Estimate ovulation date and fertile window from LMP and cycle length — see next 3 cycles predicted.

Formula: Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)

Inputs: Last menstrual period (LMP) · Cycle length (days)

Example: With LMP 2026-01-01 and 28-day cycle, ovulation around 2026-01-15, fertile window about Jan 12-17, next period Jan 29.

Field

What to enter

Last menstrual period (LMP)

Enter a value

Cycle length (days)

e.g. 28

Formula Used

Ovulation = LMP + cycleLength - 14 days; Fertile window = ovulation ± 3 days (approx)

Ovulation is estimated as 14 days before next expected period (LMP + cycleLength -14). The fertile window spans a few days before and after due to egg and sperm survival.

This is a statistical estimate, not contraception. Cycle variability, stress and health affect timing — use with cervical mucus or LH kits for better accuracy, not medical advice.

Frequently Asked Questions

QIs fertile window 6 days?

Commonly about 5 days before ovulation plus ovulation day, due to sperm living up to 5 days. This tool shows ovulation ±3 days as a simple window.

QCan this prevent pregnancy?

No, it is not contraception. Fertility awareness for contraception requires daily tracking and training.

QWhat about irregular cycles?

Use average of last 3 cycles for length, but expect wider fertile uncertainty — consult a clinician for guidance.