Due Date Calculator
Calculate your estimated due date based on last menstrual period, conception date, or IVF transfer date.
Results
Visualization
How It Works
Due dates are estimated at 280 days (40 weeks) from the last menstrual period using Naegele's rule. Only about 5% of babies are born on their due date.
The Formula
LMP Method: Due Date = LMP + 280 days + (Cycle Length - 28)
Conception: Due Date = Conception + 266 days
IVF Day 5: Due Date = Transfer + 261 days
Variables
- LMP — Last Menstrual Period — first day of your last period
- 280 — Standard gestation length in days (40 weeks)
Worked Example
LMP with 28-day cycle: Due date is 280 days (40 weeks) later. If your cycle is 32 days, add 4 extra days.
Practical Tips
- First trimester ultrasound dating is more accurate than LMP calculation.
- IVF due dates are the most precise because conception timing is known exactly.
- Longer cycles push the due date later — the formula adjusts for this.
- Most babies are born between 37 and 42 weeks.
- Your provider may adjust the due date after your dating ultrasound.