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Pregnancy Due Date Calculator
Estimate your due date, current pregnancy week, conception date, and trimester timeline using LMP, conception date, IVF transfer date, or ultrasound data.
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What Is a Pregnancy Due Date Calculator?
A pregnancy due date calculator estimates the most likely date your baby will be born — called the Estimated Due Date (EDD) or EDC (Estimated Date of Confinement). Because only about 5% of babies arrive exactly on their due date, the calculator also shows a realistic birth window from 37 to 42 weeks.
This tool supports four methods to suit every situation: Last Menstrual Period (LMP), Conception Date, IVF embryo transfer, and Ultrasound gestational age.
How Is a Due Date Calculated?
Last Menstrual Period (Naegele's Rule)
Due Date = LMP + 280 daysIf your cycle differs from 28 days, the result is adjusted by (cycleLength − 28) days.
Conception Date
Due Date = Conception + 266 daysConception typically occurs ~14 days after LMP, so this aligns with the 280-day rule.
IVF Transfer (Day 5 embryo)
Due Date = Transfer Date + 261 daysDay 3: +263d · Day 5: +261d · Day 6: +260d from transfer date.
Ultrasound Date
Due Date = (US Date − gestational days) + 280The gestational age on the scan is used to back-calculate the pregnancy start.
Pregnancy Trimesters Explained
| Trimester | Weeks | Key Developments |
|---|---|---|
| First | 1–13 | Organ formation, heart begins beating (week 6), embryo becomes fetus (week 10), risk of miscarriage highest. |
| Second | 14–27 | Movement felt (quickening ~18–20w), anatomy scan at 20w, gender can be identified, rapid growth. |
| Third | 28–40 | Brain development, lung maturation, baby positions for birth, Braxton Hicks contractions. |
IVF Due Date Calculation Explained
In IVF, the embryo age at transfer is already known, so no ovulation estimate is needed. A Day 5 (blastocyst) embryo transfer is the most common. The due date is calculated by adding 261 days to the transfer date, because the embryo is already 5 days old at transfer — equivalent to 5 days of natural development.
Day 3 transfer: Due Date = transfer date + 263 days
Day 5 transfer: Due Date = transfer date + 261 days
Day 6 transfer: Due Date = transfer date + 260 days
How Accurate Is a Due Date?
Calculated due dates are estimates, not guarantees. Only about 4–5% of babies are born on their exact EDD. Most births occur within a 2-week window either side. Early ultrasound scans (before 13 weeks) are considered the most accurate method, with a margin of error of just ±5–7 days. LMP-based calculations can be less accurate if cycles are irregular.
Example Calculation
Method: Last Menstrual Period · LMP: January 1, 2026 · Cycle: 30 days
Cycle adjustment: 30 − 28 = +2 days
Due Date: Jan 1 + 280 + 2 = October 10, 2026
Conception (estimated): Jan 1 + (30 − 14) = January 17, 2026
End of first trimester: Jan 1 + 13 weeks = April 2, 2026
Third trimester begins: Jan 1 + 28 weeks = July 16, 2026
Frequently Asked Questions
Which method is most accurate for calculating my due date?
An early ultrasound (before 13 weeks) combined with gestational age measurement is the most accurate method, with a margin of error of just ±5–7 days. LMP is the most commonly used fallback, but is less accurate if your cycles are irregular.
What if my cycle length isn't 28 days?
This calculator automatically adjusts for non-standard cycle lengths. A cycle of 30 days means ovulation occurs around day 16, so the due date shifts by +2 days. A cycle of 24 days shifts the due date by −4 days.
Can I use this calculator after a positive pregnancy test?
Yes. If you know roughly when you conceived, use Conception Date mode. If you have your LMP, use Last Period mode. Both will give you a good estimate immediately after a positive test.
What is the difference between gestational age and fetal age?
Gestational age (what doctors use) counts from the first day of your last period — so you're considered 2 weeks pregnant at the moment of conception. Fetal age (embryonic age) counts from conception itself and is always about 2 weeks less.
What does 'full term' mean?
ACOG (American College of Obstetricians and Gynecologists) defines full term as 39–40 weeks. Births at 37–38 weeks are 'early term', births at 41 weeks are 'late term', and 42+ weeks is 'post-term'. Your doctor may recommend induction after 41–42 weeks.
Can my due date change during pregnancy?
Yes. If an early ultrasound shows a gestational age significantly different from the LMP estimate (usually >5–7 days), your healthcare provider may revise your due date. This is normal and common.
Explore This Tool in Context
Pregnancy Due Date Calculator is part of the Fitness & Health collection. If you want a broader view of similar workflows, open the Fitness & Health category page or browse all QuickTools categories.
Common next steps after this tool include BMI Calculator, Calorie Calculator and Body Fat Calculator.
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