Pregnancy Due Date Calculator
This pregnancy due date calculator estimates when your baby is due, using the first day of your last menstrual period (LMP), the date of conception, an IVF embryo transfer or an ultrasound measurement. Along with the due date and its weekday, you get how far along you are, the days left, the start of each trimester and a list of milestone dates. Treat it as an estimate: the due date your OB-GYN or midwife records is the one that counts.
Updated
Results
- Day of the week
- Weeks pregnantCompleted weeks on the "as of" date
- Plus daysDays on top of the completed weeks
- Days until due dateNegative once the due date has passed
- Estimated conceptionAbout 14 days after the equivalent LMP
- Second trimester starts14 weeks 0 days
- Third trimester starts28 weeks 0 days
- Equivalent LMPThe last-period date your input corresponds to
| Weeks + days | Date |
|---|
Results are estimates. See the methodology below.
How to use the calculator
- Pick a method: first day of last period, conception date, IVF transfer of a 3-day or 5-day embryo, or ultrasound.
- Enter the date that matches the method. For an ultrasound, also enter the gestational age measured at the scan in weeks and days, exactly as written on the report.
- Adjust your cycle length under Advanced options if your period usually comes more or less often than every 28 days (21 to 45 days).
- Leave the "as of" date on today, or change it to see how far along you will be on another day.
How the due date is calculated
By convention, the estimated due date (EDD) is 280 days, or 40 weeks, after the first day of the LMP. That rule is often called Naegele's rule, which in its pencil-and-paper form subtracts 3 months and adds 7 days. It assumes a regular 28-day cycle with ovulation on day 14. The calculator counts exact days, so it can differ by a day or two from the shortcut.
Every method is first converted to an equivalent LMP:
- Last period: the date itself, shifted by (cycle length − 28) days. A 32-day cycle moves everything 4 days later, because ovulation tends to happen later in longer cycles.
- Conception: conception date − 14 days.
- IVF: transfer date − 17 days for a 3-day embryo, − 19 days for a 5-day blastocyst.
- Ultrasound: scan date minus the gestational age measured at the scan.
The due date is the equivalent LMP + 280 days. Weeks pregnant are the days from the equivalent LMP to the "as of" date, split into whole weeks plus days. The calculator marks the second trimester at 14 weeks 0 days and the third at 28 weeks 0 days.
Examples
1. Last period on August 3, 2026, 28-day cycle
The due date is Monday, May 10, 2027. On October 12, 2026 you are 10 weeks 0 days pregnant, with 210 days to go. Estimated conception: August 17, 2026. The second trimester starts November 9, 2026 and the third February 15, 2027.
2. Same last period, 32-day cycle
The equivalent LMP moves to August 7, 2026, so the due date becomes Friday, May 14, 2027. On October 12 you are 9 weeks 3 days, with 214 days left.
3. IVF, 5-day embryo transferred September 1, 2026
The equivalent LMP is August 13, 2026 and the due date is Thursday, May 20, 2027. On October 12 you are 8 weeks 4 days.
| Milestone (example 1) | Date |
|---|---|
| 12 weeks | Oct 26, 2026 |
| 20 weeks | Dec 21, 2026 |
| 37 weeks | Apr 19, 2027 |
| 40 weeks (due date) | May 10, 2027 |
| 42 weeks | May 24, 2027 |
LMP or ultrasound: which date wins?
ACOG considers an ultrasound measurement of the embryo or fetus in the first trimester, up to 13 weeks 6 days, the most accurate way to establish or confirm gestational age. Its guidance is to change the LMP-based due date when an ultrasound before 9 weeks differs by more than 5 days, or when one before 14 weeks differs by more than 7 days. After that, changes to the due date should be rare.
Say your scan on October 5, 2026 measures 9 weeks 2 days. The calculator gives Saturday, May 8, 2027, two days earlier than the LMP date in example 1. That gap is well under the 7-day threshold, so a clinician following ACOG would normally keep the LMP-based date. Your provider makes that call.
A due date is a target, not an appointment. According to MedlinePlus, a normal pregnancy can range from 38 to 42 weeks; babies born before 37 weeks are considered premature.
Frequently asked questions
How is a pregnancy due date calculated?
Add 280 days, or 40 weeks, to the first day of your last menstrual period. For other methods, the calculator first works back to an equivalent LMP.
What if my cycles are longer or shorter than 28 days?
Enter your usual cycle length under Advanced options. The calculator shifts the due date by the difference from 28 days: a 32-day cycle moves it 4 days later, a 25-day cycle 3 days earlier. With very irregular cycles, an early ultrasound is a better guide.
How do I calculate my due date after IVF?
Choose the IVF option that matches your embryo's age and enter the transfer date. ACOG recommends dating IVF pregnancies from the embryo's age and the transfer date, because the timing is known precisely.
Why is my ultrasound due date different from the LMP date?
Ovulation doesn't always happen on day 14, and period dates are easy to misremember. A first-trimester scan measures the embryo directly. StatPearls puts the margin of error of an accurate crown-rump length measurement at about 5 to 7 days, which is why small differences are usually left alone.
How many weeks pregnant am I?
The calculator shows it as weeks plus days on the "as of" date, counted from the equivalent LMP. For a week-by-week view of the pregnancy itself, our pregnancy week calculator goes into more detail.
Sources
This calculator gives an estimate for general information and is not medical advice. The due date set by your OB-GYN or midwife, usually confirmed by an early ultrasound, takes precedence.