Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date and current gestational age.
| Current gestational age | |
|---|---|
| Trimester |
How to use this tool
Enter the first day of your last menstrual period. If your average cycle isn't 28 days, adjust it — the estimate shifts by the difference from 28 days.
About this calculation
Uses Naegele's rule: due date = LMP + 280 days, adjusted for cycle length (+/- the difference from 28 days). Gestational age counts from the LMP, not from conception (which typically occurs about 2 weeks later). This is a standard obstetric estimate, not a guarantee.
This tool is for general informational purposes only and is not medical advice. Follow your doctor's or midwife's dating.
Frequently asked questions
How is the due date calculated?
Using Naegele's rule: due date = first day of the last menstrual period (LMP) + 280 days (40 weeks), assuming a typical 28-day cycle with ovulation around day 14.
How accurate is this estimate?
It's a standard estimate, not a guarantee — only a small percentage of babies are born exactly on the estimated due date. Actual delivery dates commonly range from about 3 weeks before to 2 weeks after this estimate, and your doctor may adjust it based on ultrasound dating or an irregular cycle.
Is this medical advice?
No. This is a general estimate for informational purposes only, not a medical assessment. Follow your doctor's or midwife's dating, which may use ultrasound measurements for greater accuracy.