Conception Calculator
Estimate your most likely conception date based on your due date or LMP.
Conception Calculator
Estimate your most likely conception date based on your due date or LMP.
Pregnancy Due Date — Naegele's Rule
ℹ️ Only 5% of babies are born on their exact due date. Dates are estimates only.
Disclaimer
Results provided by this calculator are for informational and educational purposes only. They are based on the values you enter and standard formulas, and should not be considered financial, medical, legal, or professional advice. Always consult a qualified professional before making important decisions based on these results. Roughtools makes no warranties regarding the accuracy or completeness of these calculations for your specific situation.
Frequently Asked Questions
Pro Tips
Only about 5% of babies are born on their due date — the Naegele's Rule date is the midpoint of a 5-week window. Don't over-plan for the exact date.
Early ultrasound (6-10 weeks) is more accurate for dating than last menstrual period if your cycles are irregular. Your OB may adjust your due date based on ultrasound.
Gestational age in weeks is counted from LMP, not conception. "6 weeks pregnant" means 6 weeks since your last period, which is only 4 weeks since likely conception.
Track your symptoms week by week using the trimester milestones. Many pregnancy apps let you export a report — useful to share with your healthcare provider.
When to Use This Calculator
Calculate your due date to plan maternity leave timing, financial preparation, and childcare arrangements.
Calculate your estimated due date in advance so you can ask the right questions at your first OB appointment.
Know your due date to schedule the baby shower at the right time — typically 4–6 weeks before delivery.
Share your due date with family and friends as a planning tool, while reminding them only 5% of babies arrive on that date.
Parents of multiple children often plan birth timing around school enrollment cutoffs — use the due date to estimate.
About the Conception Calculator
The Conception Calculator works backwards from a known due date — or forward from your last menstrual period (LMP) — to estimate when conception likely occurred. It displays the estimated ovulation window, conception date range, and a timeline of key pregnancy milestones. Results are estimates based on a standard 28-day cycle; your doctor's ultrasound dating is more accurate.
How to Use the Conception Calculator
- 1
Select your calculation method: from due date or from last period.
- 2
Enter your due date OR your last menstrual period date.
- 3
Optionally adjust your average cycle length if different from 28 days.
- 4
Click Calculate to see the estimated conception window and ovulation date.
- 5
Review the pregnancy milestone timeline below.
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