Conception Calculator
Estimated ovulation = LMP + (Cycle length − 14) daysJune 1 + (28−14) = June 15; fertile window June 10-15
Free online tool
Conception Calculator
Enter your last menstrual period date and typical cycle length.
Instant calculation
Conception Calculator
Enter your last menstrual period date and typical cycle length.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter LMP date
Type the year, month and day of your last period.
- 02
Enter cycle length
Type your typical menstrual cycle length in days.
- 03
See fertile window
Calculate to see estimated ovulation and fertile dates.
The formula
How this calculation works
Ovulation typically occurs 14 days before the next period. The fertile window is about 5 days before ovulation plus ovulation day.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
LMP June 1, 2026, 28-day cycle — when is ovulation?
June 1 + (28−14) = June 15; fertile window June 10-15Ovulation ~June 15; fertile window June 10-15Common questions
Questions about this calculation
What is the Conception Calculator?
The Conception Calculator helps you estimate your conception date and fertile window from your last period. Enter your values and select Calculate to get an instant result.
How is the result calculated?
Ovulation typically occurs 14 days before the next period. The fertile window is about 5 days before ovulation plus ovulation day.
Can you show an example?
Example: LMP June 1, 2026, 28-day cycle — when is ovulation? — Ovulation ~June 15; fertile window June 10-15.
Is my data saved when I use the Conception Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Conception Calculator free to use?
Yes. The Conception Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
Continue calculating