Pregnancy Calculator — Due Date & Milestone Tracker
A pregnancy is conventionally measured in gestational weeks — the number of weeks since the first day of the mother's last menstrual period (LMP). The standard full-term pregnancy is 40 gestational weeks (280 days from LMP), which is approximately 38 weeks from conception.
This calculator supports five common methods for estimating the due date. Each produces the same core outputs: estimated due date, current gestational age in weeks and days, trimester, a visual 40-week timeline, and a countdown to key milestones.
5 Input Methods Explained
Last Menstrual Period (LMP)
The most common method. EDD = LMP + 280 days (Naegele's rule). Adjust for non-28-day cycles: EDD shifts by the difference between your cycle length and 28.
Known Due Date
Work backwards from a known EDD to find your current gestational age and trimester. Useful if your midwife or OB has already confirmed your due date.
Ultrasound
Enter the ultrasound date and gestational age at that scan. EDD = scan date + (280 − gestational days at scan). Often more accurate than LMP for irregular cycles.
Conception Date
If you know the date of conception (ovulation day), EDD = conception date + 266 days. Conception typically occurs around day 14 of a 28-day cycle.
IVF Transfer Date
For Day 3 transfers: EDD = transfer date + 263 days. For Day 5/6 transfers: EDD = transfer date + 261/260 days. IVF gestational age counts from the equivalent LMP date.
Pregnancy Trimesters & Key Milestones
| Trimester | Weeks | Duration | Key developments |
|---|---|---|---|
| 1st | 1–12 | ~84 days | Implantation, neural tube, heartbeat (~week 6), major organ formation |
| 2nd | 13–26 | ~98 days | Anatomy scan (week 18–20), movement felt, gender visible, viability (~week 22–24) |
| 3rd | 27–40 | ~98 days | Rapid growth, lung maturation, full term at week 39–40, birth |
Frequently Asked Questions
Using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the due date shifts accordingly — for a 35-day cycle, add 7 extra days; for a 21-day cycle, subtract 7 days.
No. Gestational age is measured from the first day of the last menstrual period and is always about 2 weeks longer than fetal age (measured from conception). Doctors and pregnancy tools almost always use gestational age — so "6 weeks pregnant" means 6 gestational weeks, not 6 weeks since conception.
The first trimester runs from conception through the end of week 12 (gestational). The second trimester spans weeks 13–26. The third trimester covers weeks 27–40. These divisions vary slightly between healthcare providers — some place the second trimester start at week 14.
First-trimester ultrasounds (before 14 weeks) are considered the most accurate method for dating a pregnancy — typically within ±5–7 days. Second-trimester ultrasounds have higher variability (±1–2 weeks). If an early ultrasound contradicts the LMP date by more than 7 days, doctors typically adjust the due date.
For a Day 5 blastocyst transfer, subtract 5 days from the transfer date to get the equivalent "fertilisation date," then add 266 days for the EDD. Alternatively: EDD = transfer date + 261 days. For Day 3: EDD = transfer date + 263 days. For Day 6: EDD = transfer date + 260 days. The gestational age at transfer is already 2 weeks 3–6 days, depending on embryo age.
ACOG (American College of Obstetricians and Gynecologists) defines "full term" as 39 0/7 through 40 6/7 weeks. "Early term" is 37–38 weeks. "Late term" is 41 weeks. "Post-term" is 42 weeks or more. Babies born between 34–36 weeks are considered "late preterm."
No. This tool provides estimates for informational purposes only. Always confirm your due date, gestational age, and pregnancy milestones with your midwife, OB-GYN, or healthcare provider. Individual pregnancies vary and only a qualified professional can assess your specific situation.
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