Pregnancy Due Date Calculator
Free online pregnancy calculator. Find your due date, current week, trimester and key milestones. Enter your last period or conception date for results.
This is the first day of your last menstrual period
Usually occurs 10-14 days after the first day of LMP
Date your embryo was transferred
How Pregnancy Dating Works
Pregnancy dating is calculated using Naegele's rule, which estimates a due date 280 days (40 weeks) after the first day of your last menstrual period (LMP). This standard applies to most pregnancies, though every pregnancy is unique. Actual delivery may occur 2 weeks before or after the due date, which is why doctors consider the due date an estimate rather than a fixed date. If you know your conception date or IVF transfer date, we can also calculate your due date using those.
The Three Trimesters
| Trimester | Weeks | Key Milestones | Duration |
|---|---|---|---|
| First | 1-13 | Conception to end of first trimester. Organ systems form. Most miscarriages occur now. First ultrasound typically at 8-12 weeks. | ~13 weeks |
| Second | 14-26 | Quickening (feeling baby move). Anatomy ultrasound at 18-22 weeks. Baby develops features. Mother gains most weight. | ~13 weeks |
| Third | 27-40 | Baby gains weight rapidly. Lungs mature. Drop (lightening) occurs 2-4 weeks before labor. Braxton-Hicks contractions common. | ~14 weeks |
Important Pregnancy Dates & Guidelines
- Dating Ultrasound (8-12 weeks): Most accurate dating occurs in the first trimester. A dating ultrasound can confirm or adjust your due date.
- First Trimester Screening (11-13 weeks): Combined screening for chromosomal abnormalities.
- Anatomy Scan (18-22 weeks): Detailed ultrasound checking baby development and anatomy.
- Third Trimester (27+ weeks): Non-stress tests, monitoring for preeclampsia and other complications.
- Full Term (37+ weeks): Baby is considered full term and safe to deliver.
- Due Date (40 weeks): If labor has not started, induction may be discussed after 40 weeks.
💡 About your due date: Only about 4% of babies are born on their exact due date. The due date is an estimate, and you may deliver any time between 37 and 42 weeks. Your doctor will monitor you throughout pregnancy and adjust the due date if needed based on ultrasound findings.
⚠️ Not a medical diagnosis: This calculator provides an estimate only. Always confirm your due date with your healthcare provider. If you have any concerns about your pregnancy, contact your doctor immediately.
⭐ Why Use BestMiniApps Pregnancy Calculator?
Frequently Asked Questions
Why is the due date calculated 280 days after LMP when conception is only 266 days before birth?
Because doctors count pregnancy from the first day of your last period (not conception), which occurs roughly 14 days before actual conception. This accounts for the variability in ovulation timing. Using LMP as the reference point makes dating more consistent across all women and more accurately reflects when pregnancy is detected.
What if my due date seems wrong?
If you have irregular menstrual cycles or are unsure of your last period date, an early ultrasound (8-12 weeks) is the most accurate way to confirm your due date. Dating can also be adjusted based on later ultrasound findings, though accuracy decreases with later scans. Always discuss your due date with your healthcare provider.
Is it safe to deliver before 37 weeks?
Babies born before 37 weeks are considered preterm and may face additional health risks such as respiratory distress syndrome, feeding difficulties, and temperature regulation problems. Doctors avoid early delivery unless medically necessary. If labor starts early, you should contact your healthcare provider immediately.
What if I go past my due date?
Going past your due date is common — only 4% of babies are born exactly on the due date. A pregnancy is considered overdue (post-term) after 42 weeks, when the risk of complications increases. Your doctor will likely discuss induction options if you have not delivered by 42 weeks.
How do I calculate my due date if I had IVF?
For IVF pregnancies, your due date is calculated as 266 days from the date of transfer (for a 5-day blastocyst transfer), or adjusted based on the embryo age at transfer. Our calculator adds 266 days to the IVF transfer date. Your fertility clinic can provide the exact dating based on your specific transfer details.