Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date, how many weeks along you are today, and which trimester that falls in.
How to use the Pregnancy Due Date Calculator
- Enter the first day of your last menstrual period.
- Adjust your average cycle length if it is not 28 days.
- Read the estimated due date, your current week and trimester.
About the Pregnancy Due Date Calculator
The standard estimate adds 280 days to the first day of the last period, assuming a 28-day cycle and ovulation around day 14. If your cycles are longer or shorter, the estimate shifts, and an early ultrasound is more accurate than any date-based calculation. Fewer than one in twenty babies arrive exactly on the estimated date, so treat this as a planning guide and let your midwife or doctor confirm the dating.
Please note: this is a general wellness estimator, not a medical assessment. It does not diagnose, treat or prevent any condition, and measures like BMI are known to misclassify athletes, older adults and pregnant women. Speak to a qualified clinician about any health concern. Full disclaimer.
Frequently asked questions
How is a due date calculated?
By adding 280 days (40 weeks) to the first day of your last menstrual period — this is known as Naegele's rule.
How accurate is an estimated due date?
It is an estimate. Most births happen within two weeks either side of the date, and a dating ultrasound in the first trimester is more precise than a calculation from the last period.
What if my cycle is not 28 days?
Adjust the cycle length field. Longer cycles usually mean later ovulation, which pushes the estimated date later.
How accurate is the estimated delivery date?
It uses Naegele's rule — 280 days from the first day of your last period — which is the same method a clinic starts from. Only about one baby in twenty arrives on the estimated delivery date itself; most births happen within two weeks either side, and a dating scan is more accurate if your cycle is irregular.
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