Conception Calculator
Last Menstrual Period
How It Works
- LMP Mode: Ovulation estimated at LMP + (cycle length − luteal phase). Fertile window = 5 days before to 1 day after ovulation.
- Due Date Mode: Conception estimated 266 days before EDD. Ovulation estimated 14 days after conception.
- Ovulation Test Mode: Ovulation estimated 24–36 hours after positive LH surge. Fertile window surrounds this estimate.
- Known Conception: Due date calculated as conception + 266 days. Ideal for IVF/IUI/confirmed dates.
Overview
Use ToolYard's Conception Calculator to estimate your likely conception date and fertile window from common inputs like last menstrual period (LMP), due date (EDD), or a positive ovulation test (LH surge). Choose your mode, enter your cycle length or luteal phase if known, and get an estimated conception date, the ovulation day, and the five-day fertile window used by clinicians and fertility apps. The tool also optionally computes an estimated due date (EDD) and gestational age when possible. Calculations are private and run entirely in your browser—perfect for planning, tracking, or preparing questions for your healthcare provider.
About
About Conception Calculator
Estimate conception date and fertile window using multiple input modes.
Features:
- LMP-based conception estimation
- Due date to conception calculation
- Ovulation test (LH surge) support
- Known conception (IVF/IUI) mode
- Fertile window calculation
- Estimated due date (EDD)
- Gestational age tracking
- Fertile calendar view
- Confidence indicators
- Export to CSV
- Print summary
- 100% private - no data stored
FAQ
How accurate is this calculator?
It provides an estimate using common fertility heuristics. Ultrasound and clinical testing are more precise. Use this for planning and tracking, not clinical decisions.
What is the fertile window?
The fertile window typically includes the five days before ovulation and the day of ovulation—the timeframe when conception is most likely.
Can a positive ovulation test tell me when I conceived?
It indicates an LH surge usually 24–36 hours before ovulation. Conception may occur within the fertile window surrounding that time.
I used IVF — can I use this?
Yes. Enter your exact conception/transfer date in the 'Known Conception' mode, and the tool will compute EDD and gestational age.
What if my cycle length is irregular?
Use your average cycle length. If highly irregular, consult your healthcare provider for more personalized guidance.
Is my data stored?
No. All calculations happen in your browser and are not saved or transmitted.