👶 Pregnancy Due Date Calculator
Estimate your due date based on your last menstrual period.
28 days is the average — adjust if your cycle is typically longer or shorter.
How This Is Calculated
This calculator uses Naegele's rule — adding 280 days (40 weeks) to the first day of your last menstrual period, adjusted for cycle length if different from the 28-day average. This is a standard estimation method used widely, but only about 5% of babies are born exactly on their calculated due date.
Frequently Asked Questions
Is this calculator a substitute for medical care?
No. This tool provides a general estimate for informational purposes only. Always confirm your due date
and gestational age with your doctor or midwife, who may use ultrasound measurements for a more precise
estimate.
Guide: understanding your result
- The estimated due date is usually calculated as 280 days (40 weeks) after the first day of the last menstrual period (Naegele's rule), assuming a 28-day cycle.
- An early ultrasound, especially in the first trimester, is the most accurate way to date a pregnancy; your clinician may adjust the date based on it.
- Only a small share of babies are born on their exact due date; a full-term birth is considered 39 weeks 0 days to 40 weeks 6 days.
Worked example
If the last menstrual period began on March 1, 2026, the estimated due date is December 6, 2026; 39 weeks falls on November 29.
Pregnancy terms (ACOG)
| Term | Gestational age |
|---|---|
| Early term | 37w 0d – 38w 6d |
| Full term | 39w 0d – 40w 6d |
| Late term | 41w 0d – 41w 6d |
| Postterm | 42w 0d and beyond |
Common mistakes to avoid
- Counting from the date of conception instead of the last period — that shifts the date by about two weeks.
- Using the LMP method with very irregular or long cycles without telling your clinician.
Frequently asked questions
Is this calculator medical advice?
No. It gives an estimate for general information. Your prenatal care provider determines and, if needed, adjusts your due date.
Official sources
Examples are calculated live from the same data the calculator uses and are for education only — they are not financial, tax or investment advice.
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