Free Pregnancy Calculator Online – Due Date & Pregnancy WeeksFind your due date, how many weeks and months pregnant you are, and key dates ahead.
Your baby is due:
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Week of pregnancy
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Your pregnancy at a glance
Weekly development
Your dates are calculated in your browser and are never stored or sent anywhere.
How to use this due date calculator
Pick the method that matches what you know, enter the date, and press calculate. Most people start with the first day of their last menstrual period (LMP). If your cycle is longer or shorter than 28 days, enter your average cycle length and the estimate adjusts automatically. If you had an ultrasound or IVF, choose that method instead, as it is usually more precise.
You will see your estimated due date, how many weeks and days pregnant you are today, how many months that is, the total days and hours so far, your trimester, and a live countdown. The milestone table shows the date of each key week, such as your dating scan, anatomy scan, glucose screening and full term.
How is a pregnancy due date calculated?
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last period. This assumes a 28-day cycle and ovulation around day 14. Doctors count pregnancy from the LMP, so you are already "2 weeks pregnant" on the day you conceive.
- From LMP: due date = LMP + 280 days, adjusted by your cycle length minus 28.
- From conception: due date = conception date + 266 days.
- From ultrasound: the scan's measured gestational age is counted back to set an LMP-equivalent date. Early scans (before about 14 weeks) are the most reliable.
- From IVF: due date = transfer date + 261 days for a 5-day embryo, or + 263 days for a 3-day embryo.
Which method is the most accurate?
IVF dates are the most exact because the transfer date is known. An early ultrasound comes next, followed by a known conception date, then LMP with a regular cycle. If your LMP-based date differs from an early scan by more than about a week, your provider will usually go with the scan date.
How many weeks and months pregnant am I?
A full pregnancy lasts about 40 weeks. Because months are uneven, it works out to roughly 9 months and 1 week by the calendar, or 10 "lunar" months of 4 weeks. As a rough guide, 8 weeks is about 2 months, 20 weeks is about 4.5 months, 28 weeks is about 6.5 months, and 36 weeks is about 8.3 months.
Pregnancy trimesters at a glance
| Trimester | Weeks | What to expect |
|---|---|---|
| First | Week 1 to 13 and 6 days | Rapid early development, nausea, fatigue, first scans and blood tests |
| Second | Week 14 to 27 and 6 days | More energy, baby's movements, anatomy scan, glucose screening |
| Third | Week 28 to birth | Fast growth, more frequent checkups, preparing for labor |
Frequently asked questions
How accurate is my estimated due date?
It is an estimate, not a deadline. Only about 4 to 5 percent of babies arrive on their exact due date. Most are born between 37 and 42 weeks.
What counts as full term?
According to the American College of Obstetricians and Gynecologists, early term is 37 weeks to 38 weeks 6 days, full term is 39 weeks to 40 weeks 6 days, late term is 41 weeks to 41 weeks 6 days, and post-term is 42 weeks or more.
When does the second trimester start?
At 14 weeks 0 days. The third trimester begins at 28 weeks 0 days.
Can I use this calculator if I have irregular periods?
Enter your usual cycle length, but an ultrasound is a better guide if your cycles vary a lot. Ask your doctor or midwife to confirm your due date with a scan.
How many months is 20 weeks pregnant?
Twenty weeks is about 4 months and 2 weeks, roughly the halfway point of the pregnancy.
Why is pregnancy counted from my last period and not conception?
The date of conception is rarely known exactly, while the first day of the last period usually is. Counting from the LMP gives a consistent starting point for everyone.