Conception Calculator
Estimate your conception date from your due date or last menstrual period. Find your ovulation date and fertile window.
Part of our Health Calculators collection.
Conception Calculator
Free online calculator
Enter due date OR last period — not both
Used with last period method
Results update automatically as you type
How to Use This Calculator
- 1
Enter either your due date OR your last period date.
- 2
See estimated conception date and ovulation window.
How Conception Date is Estimated
From Due Date: Conception = Due Date − 266 days (38 weeks) Ovulation = Due Date − 280 days + 14 days From LMP: Ovulation = LMP + (Cycle Length − 14) days Conception ≈ Ovulation − 1 day
Example Calculation
Example: Due date October 8, 2025
Inputs
dueDate: 2025-10-08
Result
Conception: ~January 16, 2025
October 8 − 266 days = ~January 16.
Frequently Asked Questions
How accurate is conception date estimation?
Within ±5 days for most women with regular cycles. Conception requires sperm meeting egg during the fertile window (5 days before ovulation + ovulation day itself). The exact date is rarely pinpointable.
Can my doctor tell exactly when I conceived?
An early ultrasound (8–12 weeks) can date conception within 1–2 weeks via fetal measurements. It's more accurate than calendar methods for irregular cycles.