Pregnancy Due Date Calculator
Estimate your baby's due date and track your pregnancy timeline with key milestones
Calculate Your Due Date
Choose your calculation method below
The most common method. Enter the first day of your last menstrual period and your average cycle length.
Normal range: 21-45 days
If you know your conception date (ovulation), this method can provide a more accurate estimate.
Enter the date of your ultrasound and the gestational age measured. Early ultrasounds (before 12 weeks) are most accurate.
For IVF pregnancies, enter your transfer date and embryo age at transfer.
If you already know your due date, enter it to calculate conception date and pregnancy timeline.
How to Use This Pregnancy Calculator
- Choose your calculation method: Last Period, Conception Date, Ultrasound, IVF, or Known Due Date
- Enter the required date(s) for your chosen method
- For ultrasound, include weeks and days measured at that appointment
- Click 'Calculate Due Date' to see your full pregnancy timeline
Example: Last period: December 1, 28-day cycle. Due date: September 7. Today at week 12, you're 42% through pregnancy. First trimester ends December 23, second trimester ends March 28. Viability milestone (24 weeks) is May 17.
Tip: Early ultrasounds (before 12 weeks) are the most accurate for dating. If your ultrasound date differs from LMP by more than 5-7 days, your provider may adjust your due date.
Why Use a Pregnancy Calculator?
Knowing your due date helps you prepare for baby's arrival and lets healthcare providers monitor your pregnancy at appropriate intervals.
- Determine your estimated due date when you first suspect pregnancy
- Track your current gestational age in weeks and days
- Know when each trimester begins and ends for milestone planning
- Schedule prenatal appointments and screenings at correct gestational ages
- Plan maternity leave and baby preparations with a target date
- Understand when you'll reach key milestones like viability (24 weeks) and full-term (37 weeks)
Understanding Your Results
Results include due date, current week/day, trimester, progress percentage, key dates, and pregnancy milestones timeline.
| Result | Meaning | Action |
|---|---|---|
| Weeks 1-12 (First Trimester) | Major organ development occurs | Start prenatal vitamins, avoid alcohol/smoking, first prenatal visit |
| Weeks 13-27 (Second Trimester) | Baby grows rapidly, movements begin | Anatomy scan (20 weeks), announce pregnancy, prepare nursery |
| Weeks 28-36 (Third Trimester, Early) | Baby gains weight, lungs mature | Childbirth classes, hospital bag, finalize birth plan |
| Weeks 37-40 (Full Term) | Baby is ready for birth | Watch for labor signs, frequent check-ups, rest when possible |
Meaning: Major organ development occurs
Action: Start prenatal vitamins, avoid alcohol/smoking, first prenatal visit
Meaning: Baby grows rapidly, movements begin
Action: Anatomy scan (20 weeks), announce pregnancy, prepare nursery
Meaning: Baby gains weight, lungs mature
Action: Childbirth classes, hospital bag, finalize birth plan
Meaning: Baby is ready for birth
Action: Watch for labor signs, frequent check-ups, rest when possible
Note: Only about 4% of babies arrive on their exact due date. Consider your due date the center of a 4-week window (38-42 weeks) when baby is likely to arrive.
About Pregnancy Calculator
Formula
Due Date = LMP + 280 days (adjusted for cycle length) For conception date method: Due Date = Conception + 266 days. For IVF: Due Date = Transfer Date + (266 - embryo age). Ultrasound dating measures fetal size and back-calculates to a due date.
Current Standards: Full-term pregnancy: 39-40 weeks. Early term: 37-38 weeks. Late term: 41 weeks. Post-term: 42+ weeks. Most providers offer induction between 41-42 weeks as stillbirth risk increases after 42 weeks.
Frequently Asked Questions
How accurate is my due date?
First-trimester ultrasounds predict due dates within 5-7 days. LMP calculations can be off by 1-2 weeks if ovulation timing was unusual. Only 4% of babies arrive on their exact due date, but 80% arrive within 2 weeks of it. IVF due dates are most precise because transfer date is exact. Consider your due date an estimate, not an appointment.
Will my due date change?
It might. If an early ultrasound (ideally before 12 weeks) differs from your LMP-based date by more than 5-7 days, most providers will adjust your due date to match the ultrasound. Later ultrasounds aren't used for dating because fetal growth varies too much. Once established in the first trimester, your due date typically stays fixed even if later measurements differ.
What if I don't know my last period date?
If LMP is unknown or your cycles were irregular, an early ultrasound becomes essential for dating. Ultrasound measurements before 12 weeks are accurate within days because embryos at the same gestational age are very similar in size - individual growth variation hasn't yet begun. Dating ultrasounds become less accurate as pregnancy progresses.
How is pregnancy counted - from conception or LMP?
Pregnancy weeks are counted from LMP, not conception. This seems counterintuitive since you weren't pregnant during your period, but it's the medical standard because LMP date is typically known while conception date is not. So at 'week 2' of pregnancy, conception is just occurring. When your baby is born at '40 weeks,' actual fetal age is about 38 weeks.
What happens if I go past my due date?
Most providers allow pregnancy to continue until 41-42 weeks before recommending induction, as long as baby and mother are healthy. After 42 weeks, risks of stillbirth and complications increase significantly. You'll have more frequent monitoring (non-stress tests, fluid checks) after 40 weeks. 50% of first-time mothers deliver after their due date - it's common, not necessarily concerning.