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?
Your due date is a careful estimate, not a fixed appointment. It marks the center of a likely birth window rather than a guaranteed date — only about 4% of babies actually arrive on it, while most arrive within a couple of weeks on either side. A due date based on your last menstrual period can be off if ovulation happened earlier or later than the usual day 14, especially with irregular cycles. A first-trimester ultrasound, which measures the baby's size before individual growth differences emerge, is the most accurate dating method and is typically precise within several days. IVF dates tend to be the most exact because the transfer date is known. Your doctor or midwife confirms your dating.
Will my due date change?
It can, usually early in pregnancy. If a first-trimester ultrasound (ideally before 12 weeks) differs from your last-menstrual-period date by more than about a week, many providers adjust the due date to match the ultrasound, since early measurements are more reliable than recalled period dates. Once your due date is established in the first trimester, it generally stays fixed for the rest of the pregnancy, even if later scans show the baby measuring larger or smaller — that reflects normal variation in growth, not a change in age. Later ultrasounds are not used to redate a pregnancy because growth differences widen over time. Your provider decides whether any adjustment is appropriate for your situation.
What if I don't know my last period date?
An early ultrasound can date the pregnancy when your last period is unknown. If you do not remember your LMP, or your cycles were irregular and the date is unreliable, a first-trimester ultrasound becomes the primary dating tool. Measurements taken before about 12 weeks are accurate within days, because at the same gestational age early embryos are very similar in size and individual growth variation has not yet begun. As pregnancy advances, babies grow at increasingly different rates, so ultrasounds done later in pregnancy are less precise for dating. If your LMP is uncertain, mention it to your doctor or midwife, who can arrange an early scan to establish your timeline.
How is pregnancy counted - from conception or LMP?
Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. This can seem odd, since you were not yet pregnant during your period, but it is the accepted medical standard because the LMP date is usually known while the exact moment of conception is not. With a typical 28-day cycle, ovulation and conception occur around two weeks into the count, so at 'week 2' conception is roughly just happening. That two-week offset carries through the whole pregnancy: when a baby is born at '40 weeks' of gestational age, the actual age since conception is about 38 weeks. Counting from a consistent, knowable starting point keeps prenatal milestones and screening schedules aligned.
What happens if I go past my due date?
Going past your due date is common and not necessarily a concern. Many first-time mothers deliver after their due date, which is why the date is treated as the middle of a window rather than a deadline. When a pregnancy continues beyond term, providers usually increase monitoring — such as non-stress tests and checks of amniotic fluid — to confirm the baby is doing well. Because the risk of complications rises the further a pregnancy goes past term, providers commonly discuss induction around 41 to 42 weeks, weighing your individual circumstances. There is no single right answer for everyone. Your doctor or midwife will explain the options and recommend the timing that is safest for you and your baby.