Pregnancy Due Date Calculator
Calculate your expected delivery date, current trimester, and week-by-week pregnancy timeline from your last menstrual period
Your Results
Enter your last menstrual period date and click Calculate.
Pregnancy Timeline
| Trimester | Weeks | Key Milestones |
|---|---|---|
| 1st Trimester | Weeks 1–12 | Implantation, heartbeat detected (~week 6), major organs form |
| 2nd Trimester | Weeks 13–26 | Baby moves (~week 18–20), gender visible on ultrasound, rapid growth |
| 3rd Trimester | Weeks 27–40 | Baby gains weight, lungs mature, head engages, birth preparation |
Frequently Asked Questions
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle. If your cycle is longer or shorter, the calculator adjusts by adding or subtracting the difference from 28 days.
Only about 5% of babies are born exactly on their due date. Most births occur within 2 weeks before or after the estimated due date. A full-term pregnancy is considered anywhere from 39 to 40 weeks and 6 days. An early ultrasound (between 8–13 weeks) provides the most accurate dating.
LMP stands for Last Menstrual Period. Since the exact date of conception is rarely known, doctors count from the first day of your last period. Ovulation typically occurs about 14 days after LMP, so actual conception is roughly 2 weeks after the LMP date.
The first trimester runs from weeks 1–12, the second from weeks 13–26, and the third from weeks 27–40. The first trimester is the most critical for fetal development, when major organs and systems are forming.
If you don't know your LMP date, you can use the conception date option in this calculator if you know when conception occurred. Alternatively, a doctor can estimate gestational age through an ultrasound, which measures the size of the embryo or fetus.
About This Pregnancy Due Date Calculator
This free Pregnancy Due Date Calculator uses Naegele's Rule — the same method used by doctors worldwide. Enter the first day of your last menstrual period to get your estimated due date, current weeks pregnant, trimester, and key milestone dates. Supports variable cycle lengths between 21 and 35 days.
Weeks Pregnant Reference
| Weeks | Trimester | Approx. Size |
|---|---|---|
| 4 weeks | 1st | Poppy seed |
| 8 weeks | 1st | Raspberry |
| 12 weeks | 1st | Lime |
| 16 weeks | 2nd | Avocado |
| 20 weeks | 2nd | Banana |
| 24 weeks | 2nd | Corn |
| 32 weeks | 3rd | Squash |
| 40 weeks | 3rd | Watermelon |
Key Milestone Dates
| Milestone | Typical Week |
|---|---|
| Heartbeat detectable | Week 6 |
| End of 1st trimester | Week 12 |
| Anatomy scan (ultrasound) | Week 18–20 |
| Viability milestone | Week 24 |
| End of 2nd trimester | Week 26 |
| Early term birth | Week 37 |
| Full term birth | Week 39–40 |
