Pregnancy Due Date Calculator – Estimate Your Week, Trimester & Baby’s Milestones
The Pregnancy Due Date Calculator from FreeFitnessCalculators.com helps you discover your expected due date (EDD), conception date, current week, and trimester — all in one easy step. Simply enter your last menstrual period, conception, ultrasound, or IVF transfer date to instantly reveal your pregnancy timeline and baby’s progress.
This calculator uses the same medical standards applied by ACOG (American College of Obstetricians and Gynecologists) and the World Health Organization (WHO), providing accurate estimates for a full-term pregnancy of approximately 40 weeks (280 days).
Beyond just numbers, it also highlights key fetal milestones — from implantation and heartbeat detection to gender reveal and full-term growth. Whether you’re newly expecting or tracking week by week, this tool gives clear, compassionate, and science-based insights.
How to Use the Pregnancy Due Date Calculator
- Select a method — LMP, Ultrasound, Conception, or IVF Transfer.
- Enter the date requested (e.g., your last period or scan date).
- If applicable, choose your cycle length or embryo type.
- Click Calculate to view your complete pregnancy overview.
You’ll instantly see your estimated due date, conception date, current week & day, trimester, and progress percentage toward full term. Plus, visual milestone cards show upcoming fetal developments.
What Is a Due Date?
Your Estimated Date of Delivery (EDD) is the projected day your baby is likely to be born. It marks the completion of 40 weeks (280 days) of pregnancy, measured from the first day of your last menstrual period — not the day you conceived.
Because ovulation typically occurs around day 14 of the cycle, this method adds about two weeks before conception. While not precise for every woman, it provides a medically standardized baseline that aligns with ultrasound data and global obstetric practice.
Different Ways to Calculate Your Due Date
Our calculator supports all recognized clinical methods of pregnancy dating:
- LMP (Last Menstrual Period): The most common and reliable if your cycles are regular (around 28 days).
- Ultrasound Dating: Uses fetal size during early scans (typically 8–12 weeks) to estimate gestational age.
- Conception Date: Best if you know exactly when fertilization occurred (for example, through ovulation tracking or IVF).
- IVF Transfer Date: Adds precise offsets based on embryo age — Day 3 or Day 5 blastocyst transfer.
Each method ultimately points to the same goal — an accurate view of your pregnancy’s progress and your baby’s likely arrival window.
The Standard Due Date Formula
The most widely used calculation is Naegele’s Rule:
Due Date = LMP + 280 days (40 weeks)
For conception-based calculation:Due Date = Conception Date + 266 days
IVF pregnancies use slightly modified equations to account for embryo development:Due Date = Transfer Date + (280 − (Embryo Day + 14))
The calculator automatically applies the correct formula for your chosen method.
Pregnancy Timeline by Trimester
| Trimester | Weeks | Highlights |
|---|---|---|
| First | 1–13 | Implantation, heartbeat detection, organ formation. |
| Second | 14–27 | Baby movements, gender reveal, growth acceleration. |
| Third | 28–40 | Rapid weight gain, lung maturity, preparation for birth. |
Each trimester marks a new phase of growth for your baby and your body’s adaptation. By week 20, many expectant mothers begin to feel kicks and flutters — a beautiful reminder of life growing within.
Baby Growth & Milestones
Your baby develops at an incredible rate. Here’s a glimpse of what happens week by week:
| Week | Milestone |
|---|---|
| 4 | Implantation complete, positive pregnancy test possible. |
| 6 | Heartbeat detectable via ultrasound. |
| 9 | Facial features and major organs begin forming. |
| 12 | First trimester ends; risk of miscarriage decreases. |
| 20 | Gender usually visible; anatomy scan performed. |
| 28 | Third trimester begins; baby opens eyes and reacts to light. |
| 37 | Full term begins; baby ready for delivery anytime now. |
Our calculator includes visual indicators for milestones like heartbeat detection, organ formation, and baby movements — giving you an easy way to see what’s next in your pregnancy journey.
How Accurate Are Pregnancy Due Dates?
Due dates are estimates — not guarantees. Only about 4% of babies are born exactly on their due date. Most arrive within a two-week window before or after.
Early ultrasounds are the most accurate for dating because fetal growth rates vary later in pregnancy. Your provider may adjust your due date if ultrasound results differ significantly from your LMP estimate.
💡 Tip: Use the calculator’s progress bar to visualize your current stage — a 50% mark means you’re halfway through your pregnancy!
When Due Dates Change
It’s common for doctors to refine your due date after your first ultrasound. Adjustments happen if:
- The baby measures smaller or larger than expected.
- You have irregular cycles or uncertain ovulation dates.
- Implantation occurred later than average.
Even with changes, the difference is typically just a few days — your healthcare team will keep you informed at every stage.
Frequently Asked Questions
How long is pregnancy?
On average, a full-term pregnancy lasts 40 weeks, or about 9 months from your last period.
Can my due date be wrong?
Small differences are normal. Ultrasound dating within the first trimester is considered most accurate.
Can I have a due date if my cycle is irregular?
Yes. Use the conception or ultrasound option in the calculator for more accurate results.
When does the third trimester begin?
The third trimester starts at week 28 and lasts until delivery (week 40).
What is considered full term?
Between 37 and 42 weeks of gestation. Babies born in this range are generally healthy and fully developed.
Does IVF affect due date accuracy?
IVF pregnancies are the most precise since the exact fertilization and embryo transfer dates are known.
References & Further Reading
- American College of Obstetricians and Gynecologists (ACOG) Committee Opinion No. 700: Methods for Estimating the Due Date.
- World Health Organization (WHO) Fetal Growth Charts: Multinational Study of Ultrasound Biometric Measurements.
- Cleveland Clinic – Due Date Calculator: Determining Gestational Age and EDD.
- NHS – Pregnancy Due Date Calculator: Calculating Your Estimated Date of Delivery.
The Due Date Calculator is based on established obstetrical standards, including the ACOG Committee Opinion No. 700 and the **Naegele's rule** for calculating 40 weeks (280 days) from the Last Menstrual Period (LMP). It incorporates data from the WHO Fetal Growth Charts to model the most accurate date range, acknowledging that **first-trimester ultrasound** remains the gold standard for clinical dating. The calculator's predicted outcomes align with the consensus on 'term' pregnancy duration, as established by leading medical research and bodies.
Conclusion
The Pregnancy Due Date Calculator combines medical precision with an intuitive interface to help you stay informed and reassured throughout your pregnancy. Whether you calculate from your period, ultrasound, or IVF transfer, it delivers accurate insights instantly.
Use it together with our Pregnancy Weight Gain and Sleep Quality Index calculators for a complete prenatal wellness toolkit.
At FreeFitnessCalculators.com, our mission is to make health data clear, credible, and empowering — because every expecting parent deserves confidence through knowledge. Track, learn, and celebrate every milestone of your beautiful journey to birth.