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.

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.

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.

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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

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.