Ovulation & Fertile Window Calculator
Calculate ovulation day, fertile window, next period, and estimated pregnancy due date.
- 100% free
- Private in browser
- No signup
- No watermarks
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About Ovulation & Fertile Window Calculator
Estimate your fertile window and ovulation day to plan pregnancy or track menstrual cycles. Enter the first day of your last period and your average cycle length to receive an instant fertile calendar breakdown.
How to use Ovulation & Fertile Window Calculator
- Select the first day of your last menstrual period (LMP).
- Select your average cycle length (typically 28 days).
- View your estimated Ovulation Day, Most Fertile Window (6 days), and Next Period Date.
Key features
- Accurate ovulation day prediction (14 days before next period)
- Calculates 6-day fertile window (5 days prior + ovulation day)
- Estimates next expected menstrual period date
- Calculates estimated due date if conception occurs
- 100% private, no tracking or personal data stored
Frequently asked questions
- When does ovulation occur?
- Ovulation typically occurs around 14 days before the start of the next menstrual period. In a 28-day cycle, this is around Day 14.
- What is the fertile window?
- The fertile window encompasses the 5 days before ovulation and the day of ovulation itself, because sperm can survive in the reproductive tract for up to 5 days.
- What do I need to enter?
- Just First Day of Last Period and Average Cycle Length. Every field has a sensible default you can start from.
- Is my data uploaded anywhere?
- No. The calculation runs in your browser with JavaScript — nothing you type is sent to a server or stored.
- Does it work on a phone?
- Yes. The layout adapts to small screens and needs no app or signup.
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