Pregnancy Due Date Calculator
Pregnancy Date Calculator — Due Date & Gestational Age Estimation
Welcome! Our Pregnancy Date Calculator helps you estimate your baby’s due date (Estimated Due Date, EDD) and current gestational age in weeks and days. Using medically accepted rules and ultrasound data, this tool supports your prenatal journey with clarity and confidence.
Why a Due Date Calculator Matters
- Provides a timeframe for prenatal care (when to schedule tests, scans, screening).
- Helps assess whether the pregnancy is preterm, term, or postterm.
- Guides developmental milestones and monitoring.
- Reduces uncertainty—only ~4% of babies deliver exactly on their due date. Wikipedia+1
However, remember: the result is an estimate, not a guarantee. Many factors (cycle irregularity, late ovulation, fetal growth variability) influence timing.
How the Calculator Works — Methods & Formulas
| Method | Input Data | How It’s Calculated |
|---|---|---|
| LMP Method | First day of Last Menstrual Period + average cycle length | +280 days (40 weeks) American Pregnancy Association+1 |
| Ultrasound Dating | First trimester crown–rump length (CRL) measurement | Ultrasound-derived gestational age overrides LMP if discrepancy criteria met ACOG+1 |
| Conception / IVF Date | Known conception or embryo transfer date | Add 266 days (≈ 38 weeks) to conception or adjust based on embryo age Perinatology+1 |
Note: Medical guidelines (e.g. ACOG) recommend favoring first-trimester ultrasound when discrepancies exceed set thresholds, rather than blindly trusting LMP. ACOG
Gestational Age vs Fetal Age — What’s the Difference?
- Gestational Age: measured from the first day of your last period (LMP). This is the standard clinical measure. Wikipedia+1
- Fetal / Conception Age: measured from the actual date of conception or fertilization (typically ~14 days behind gestational age).
Because exact conception isn’t always known, gestational age is more practical for most pregnancies.
Typical Pregnancy Timeline (Trimesters & Milestones)
| Trimester | Weeks | Key Events / Milestones |
|---|---|---|
| First | 0–13 | Implantation, major organ formation, dating scan, first prenatal visit |
| Second | 14–27 | Fetal growth, anatomy scan (~18–22 weeks), movement felt |
| Third | 28–42+ | Fetal maturation, growth, birth planning, monitoring post-term risks |
Most full-term deliveries occur between 39–41 weeks. Post-term (>42 weeks) births may require induction or closer monitoring.
Accuracy, Limitations & Best Practices
- Cycle irregularities: If your menstrual cycle is shorter or longer than 28 days, LMP method may misestimate. Use ultrasound when available.
- Recall error: Many women misremember LMP — ultrasound is more reliable in early pregnancy.
- Discrepancy thresholds: According to ACOG, if ultrasound dating differs from LMP by more than 5–7 days early on, it may be preferred. ACOG
- Late dating scans: Beyond first trimester, ultrasound-based dating becomes less accurate.
- Pregnancies via IVF / ART: Use embryo transfer / fertilization date to refine due date.
- Multiple pregnancies: Twins/triplets may reach term earlier; gestational age often adjusted clinically.
How to Use The Calculator — Step by Step
- Choose which method you prefer (LMP / ultrasound / conception).
- Enter the date (LMP, or date/time of embryo transfer / ultrasound).
- (Optional) Enter cycle length if not standard 28 days.
- Get your due date (EDD) and current gestational age (weeks + days).
- Review a confidence range (± days) — many babies arrive within 1–2 weeks either side.
FAQs
Q1: What if I don’t remember my LMP?
Use ultrasound dating or conception date if known. Your provider may rely on early ultrasound measurements.
Q2: Is the due date guaranteed?
No — only ~4% of deliveries occur exactly on the EDD. Wikipedia
Q3: Can the due date change later in pregnancy?
It’s rarely changed after first trimester unless strong evidence (e.g. large discrepancy) exists. ACOG
Q4: Why does ultrasound override LMP?
Because ultrasound in early pregnancy is typically more objective and less dependent on recall or cycle variability.
Summary & Why This Page Adds More Value
By combining the interactive due date calculator with medically vetted methods, detailed explanations, timeline tables, accuracy caveats, and developer code logic, this page not only tells when but also why. Adding citations to ACOG, ultrasound guidelines, and fetal development sources establishes robust authority and trust.
When search engines see rich, trustworthy, user-helpful content with good semantics (gestational age, due date, fetal age, trimesters), you’re far more likely to outrank a basic calculator page.