Due Date Calculator
Calculate pregnancy due date using Naegele's Rule.
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How This Due Date Calculator Works
This calculator uses established scientific formulas validated in peer-reviewed literature. All calculations run locally in your browser — no data is sent to any server.
Pregnancy Timeline
| Trimester | Weeks | Key Developments | Extra Calories |
|---|---|---|---|
| First | 1–13 | Organ formation | +0 cal/day |
| Second | 14–27 | Growth, movement | +340 cal/day |
| Third | 28–40 | Weight gain, positioning | +450 cal/day |
During pregnancy, use the Calorie Calculator with trimester adjustments. Increase protein for fetal growth. Stay hydrated with the Water Intake Calculator. Note that BMI interpretation changes during pregnancy.
How Naegele's Rule Works
Naegele's Rule, developed by German obstetrician Franz Karl Naegele in the early 1800s, adds 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a 28-day menstrual cycle with ovulation occurring on day 14. If calculating from a known conception date, the formula adds 266 days (38 weeks) since conception occurs approximately 14 days after the LMP in a typical cycle.
Only about 4% of babies arrive on their exact due date. The majority (approximately 80%) are born within 2 weeks before or after the estimated due date. Factors that influence actual delivery timing include whether this is a first pregnancy (first babies tend to arrive slightly later), maternal age, genetics, and overall health.
Nutrition During Pregnancy by Trimester
Calorie needs change as pregnancy progresses. In the first trimester, no additional calories are typically needed — focus on nutrient density rather than quantity. In the second trimester, an additional 340 calories per day supports fetal growth and increased blood volume. In the third trimester, approximately 450 extra calories per day are recommended. Use the Calorie Calculator with these adjustments.
Protein requirements increase to approximately 1.1g per kg of body weight during pregnancy (up from 0.8g/kg). Iron, folate, calcium, and omega-3 fatty acid needs also increase. Stay well-hydrated with an additional 24-32 oz of water per day — check your baseline with the Water Intake Calculator.
Note that standard BMI interpretation does not apply during pregnancy. Weight gain of 25-35 lbs is recommended for women starting at a normal BMI, 15-25 lbs for those starting overweight, and 28-40 lbs for those starting underweight.
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