Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date and how far along you are, using the standard 280-day (40-week) method.
Pregnancy Due Date Calculator
Estimates your baby's due date and current weeks pregnant from the first day of your last menstrual period.
This calculator uses Naegele's rule — the standard obstetric method of adding 280 days (40 weeks) to the first day of your last menstrual period — to estimate a due date, and also reports how many weeks pregnant you are as of today. It's the same basic calculation used as a starting point in most prenatal care, though your healthcare provider may refine the estimate using ultrasound dating, especially if your cycle length differs from the typical 28 days.
Example
- With the default values shown above, this calculator returns: Estimated Due Date = 2027-06-18; Weeks Pregnant Today ≈ 0 weeks.
Frequently Asked Questions
How is the due date calculated?
It uses Naegele's rule, the standard obstetric estimate of adding 280 days (40 weeks) to the first day of your last menstrual period, assuming a typical 28-day cycle.
Is this due date exact?
No — it's a standard estimate. Only a small percentage of babies are born exactly on their estimated due date; your healthcare provider may adjust the estimate using ultrasound measurements.
What if my cycle isn't 28 days?
This calculator uses the standard 28-day-cycle assumption; if your cycles are consistently longer or shorter, your actual due date may differ — your healthcare provider can adjust for this.
Sources
- Standard formula, publicly documented method