Due Date Calculator
Calculate your due date, current week, and trimester based on the first day of your last period.
Input Information
* Due date is calculated as 280 days (40 weeks) from the first day of the last period.
Result
Accurately calculate your due date!
The due date calculator computes your expected delivery date based on the first day of your last menstrual period (LMP). Medically, pregnancy duration is calculated as 280 days (40 weeks) from the LMP.
The calculated due date is an estimate. The actual delivery date may differ by about ±2 weeks. Deliveries between weeks 37-42 are considered full-term and normal.
It shows your current week, trimester, and provides weekly milestones and fetal development status to help you manage your pregnancy.
Term Glossary
- Due Date (EDC)
- Estimated Date of Confinement. Set 280 days (40 weeks) from the first day of the last period. Actual delivery may vary ±2 weeks.
- Trimester
- Pregnancy divided into three periods: 1st (weeks 1-12), 2nd (weeks 13-26), 3rd (weeks 27-40).
- Full Term
- Weeks 37-42 of pregnancy. Deliveries during this period are considered medically normal.
- LMP (Last Menstrual Period)
- The first day of the last menstrual period. Serves as the reference point for calculating pregnancy weeks.
- Select LMP date → Enter the first day of your last menstrual period
- Calculate → Click the Calculate button
- View results → Check your estimated due date (EDC), current week, and trimester information
LMP: January 1, 2025
Due Date = Jan 1, 2025 + 280 days = October 8, 2025
LMP: June 15, 2025
Due Date = Jun 15, 2025 + 280 days = March 22, 2026
Due Date Calculation Formula
Basic Formula (Naegele's Rule)
Due Date = LMP + 280 days (40 weeks)Alternatively: subtract 3 months from LMP month and add 7 days.
Example: LMP = January 15, 2026 → Due Date = October 22, 2026Trimester Breakdown
- 1st Trimester (Weeks 1-12): Organ formation, highest miscarriage risk
- 2nd Trimester (Weeks 13-26): Fetal growth, relatively stable period
- 3rd Trimester (Weeks 27-40): Fetal maturation, birth preparation
Fetal Size Comparison
- 4 weeks: Poppy seed (1-2mm)
- 8 weeks: Blueberry (1.5-2cm)
- 12 weeks: Lemon (5-6cm)
- 20 weeks: Banana (25cm)
- 28 weeks: Leek (35cm)
- 36 weeks: Lettuce (47cm)
- 40 weeks: Watermelon (50-52cm)
Key tips for pregnancy management
1. Don't miss regular checkups
1st trimester: every 4 weeks; 2nd: every 2-3 weeks; 3rd: weekly checkups are recommended. Monitor fetal growth and maternal health.
2. Start folic acid and iron supplements
Early pregnancy requires folic acid (400-800μg/day) for neural tube defect prevention. From the 2nd trimester, iron supplementation helps prevent anemia.
3. Maintain appropriate weight gain
Weight gain varies by pre-pregnancy BMI. For normal weight, 11.5-16kg during pregnancy is appropriate.
4. Exercise gently
Walking, swimming, and light yoga are recommended during pregnancy. Avoid high-intensity or high-impact activities.
5. Prepare emergency contacts
In the 3rd trimester, prepare your delivery hospital contact, emergency contacts, and hospital bag in advance so you can respond immediately when labor begins.
QHow accurate is the estimated due date?
The EDC has a margin of ±2 weeks (±14 days). Only about 5% of deliveries occur on the exact due date.
QWhat are the limitations of Naegele's Rule?
Accuracy decreases with irregular cycles, uncertain ovulation, or multiple pregnancies. Ultrasound dating may be more accurate.
QHow is gestational age calculated?
Days elapsed since the first day of the last menstrual period (LMP) divided by 7. Medically, LMP is considered week 1, day 0.
QWhat defines a preterm delivery?
Delivery before 37 weeks of gestation is classified as preterm. Before 32 weeks is very preterm; 24–37 weeks is moderate to late preterm.
QWhat are the risks of post-term pregnancy (42+ weeks)?
Risks include declining placental function, low amniotic fluid, macrosomia, and cord complications. Induction is typically considered between 41–42 weeks.