Due Date Calculator
Your estimated due date is 280 days (40 weeks) after the first day of your last period, adjusted if your cycle is longer or shorter than 28 days. Enter your last period, conception date, IVF transfer date or ultrasound result to see your due date, how many weeks pregnant you are today and the dates of key milestones.
By the Calculators With Steps team · Updated November 10, 2026 · How we check our math
- How far along today
- 10 weeks, 0 days
- Trimester
- First trimester
- Days until due date
- 210 days30 weeks, 0 days to go
- Estimated conception
- Sep 15, 2026Due date − 266 days
- Pregnancy week 1 began
- Sep 1, 2026Counted from the (equivalent) first day of the last period
- Full-term window (39w 0d – 40w 6d)
- Jun 1 – Jun 14, 2027
Step-by-step working
- First day of last period Sep 1, 2026 + 280 days (40 weeks) = Jun 8, 2027
- 28-day cycle, so no adjustment is needed
- Today (Nov 10, 2026) is 70 days after the pregnancy start date of Sep 1, 2026 = 10 weeks, 0 days
Pregnancy milestones
| Milestone | Gestational age | Date |
|---|---|---|
| Pregnancy week 1 begins | 0w 0d | Sep 1, 2026 |
| Estimated conception | 2w 0d | Sep 15, 2026 |
| End of first trimester | 13w 6d | Dec 7, 2026 |
| Second trimester begins | 14w 0d | Dec 8, 2026 |
| Anatomy scan window | 18w 0d – 22w 6d | Jan 5 – Feb 8, 2027 |
| Viability milestone (about 24 weeks) | 24w 0d | Feb 16, 2027 |
| Third trimester begins | 28w 0d | Mar 16, 2027 |
| Early term | 37w 0d – 38w 6d | May 18 – May 31, 2027 |
| Full term | 39w 0d – 40w 6d | Jun 1 – Jun 14, 2027 |
| Estimated due date | 40w 0d | Jun 8, 2027 |
| Late term | 41w 0d – 41w 6d | Jun 15 – Jun 21, 2027 |
| Postterm begins | 42w 0d | Jun 22, 2027 |
Gestational age is counted from the first day of the last period, about two weeks before conception. A due date is an estimate: most babies arrive between 37 and 42 weeks. A first-trimester ultrasound is the most accurate way to date a pregnancy, so your midwife or doctor may adjust this date after a scan.
How to use the due date calculator
- Pick what you know: the first day of your last period (LMP), the conception date, your IVF embryo transfer date, or the gestational age from an ultrasound.
- Enter the date. For the LMP method, also enter your average cycle length (leave it at 28 if you are not sure). For IVF, choose a day-3, day-5 or day-6 embryo. For a scan, enter the weeks and days written on the report.
- Read your estimated due date, how far along you are today, your trimester and a table of milestone dates.
All four methods give the same answer for the same pregnancy, so you can cross-check one against another.
How the due date is calculated
Pregnancy is counted from the first day of the last period, about two weeks before conception. That is why a full-term pregnancy is described as 40 weeks even though the baby develops for about 38.
From your last period (Naegele’s rule): due date = LMP + 280 days + (cycle length − 28)
From conception: due date = conception date + 266 days
From IVF transfer: due date = transfer date + (266 − embryo age in days), which is 263 days for a day-3 embryo, 261 for a day-5 blastocyst and 260 for a day-6 blastocyst
From an ultrasound: due date = scan date + (280 − gestational age at the scan in days)
The IVF rule follows from conception. A day-5 embryo was fertilised five days before it was transferred, so 266 − 5 = 261 days remain. ACOG uses exactly these numbers for pregnancies conceived with assisted reproduction.
If you track dates in a spreadsheet, the due date formula in Excel or Google Sheets is =A2+280+(B2-28), with the LMP in A2 and the cycle length in B2. Format the result cell as a date.
Worked example: one pregnancy, four methods
Say a last period started on Monday, January 5, 2026 and cycles are 28 days long. Here is how each method lands on the same date.
| Method | Date entered | Days added | Due date |
|---|---|---|---|
| Last period (LMP) | Jan 5, 2026 | 280 | Mon, Oct 12, 2026 |
| Conception | Jan 19, 2026 | 266 | Mon, Oct 12, 2026 |
| Day-5 IVF transfer | Jan 24, 2026 | 261 | Mon, Oct 12, 2026 |
| Day-3 IVF transfer | Jan 22, 2026 | 263 | Mon, Oct 12, 2026 |
| Ultrasound at 9w 0d | Mar 9, 2026 | 217 | Mon, Oct 12, 2026 |
With a 32-day cycle instead, ovulation is likely 4 days later, so the due date moves to Friday, October 16, 2026.
Pregnancy milestones by week
For the same January 5, 2026 last period, the calculator lists these dates. Use the table in your results to see your own.
| Milestone | Gestational age | Date |
|---|---|---|
| End of first trimester | 13w 6d | Apr 12, 2026 |
| Second trimester begins | 14w 0d | Apr 13, 2026 |
| Anatomy scan window | 18w 0d – 22w 6d | May 11 – Jun 14, 2026 |
| Viability milestone | 24w 0d | Jun 22, 2026 |
| Third trimester begins | 28w 0d | Jul 20, 2026 |
| Early term | 37w 0d – 38w 6d | Sep 21 – Oct 4, 2026 |
| Full term | 39w 0d – 40w 6d | Oct 5 – Oct 18, 2026 |
| Late term | 41w 0d – 41w 6d | Oct 19 – Oct 25, 2026 |
The term labels come from ACOG, which replaced the single word “term” with early, full, late and postterm because research showed that outcomes for babies, especially breathing problems, vary across those five weeks.
Which date should you trust?
- A first-trimester ultrasound wins. Measuring the embryo before 14 weeks is the most accurate dating method. If the scan and your LMP date disagree by more than a few days, your doctor or midwife will usually go with the scan. In the UK, the NHS offers a dating scan at around 12 weeks for this reason.
- IVF dates are precise. The fertilisation date is known, so the transfer-based date is used for assisted pregnancies.
- LMP dates work best with regular cycles. If your cycles are irregular, you are unsure of the date, or you conceived soon after stopping hormonal contraception, an ultrasound is more reliable.
- Once set, the date rarely changes. ACOG advises against changing the due date later in pregnancy except in rare cases, because later scans measure growth as much as age.
Tips for using your due date
- Treat it as the middle of a window. Plan around the full-term range rather than a single day.
- Add your anatomy scan window to your calendar early, since appointments fill up.
- Track your weight and nutrition with the BMI calculator and water intake calculator, and ask your provider what gain is right for you.
- Trying to conceive? The ovulation calculator shows your fertile window and the due date for each cycle.
- To count the days between any two dates, use the days between dates calculator.
Due Date Calculator: frequently asked questions
How is a due date calculated?
Add 280 days (40 weeks) to the first day of your last menstrual period. This is called Naegele's rule. If your last period started on January 5, 2026, your estimated due date is Monday, October 12, 2026. Add or subtract days if your cycle is longer or shorter than 28 days.
How do I calculate my due date from the conception date?
Add 266 days (38 weeks) to the conception date. Conception on January 19, 2026 gives a due date of October 12, 2026. Doctors still describe the pregnancy in weeks from the last period, so on the day of conception you count as 2 weeks pregnant.
How do you calculate an IVF due date?
Count from the embryo transfer date. Add 261 days for a day-5 blastocyst, 263 days for a day-3 embryo and 260 days for a day-6 blastocyst. A day-5 transfer on January 24, 2026 gives a due date of October 12, 2026.
How many weeks pregnant am I?
Count the days from the first day of your last period to today and divide by 7. If your last period began on January 5, 2026, then on March 9, 2026 you are 63 days, or exactly 9 weeks 0 days, pregnant. The calculator shows this for today automatically.
What if my cycle is longer than 28 days?
Ovulation usually happens later in a longer cycle, so the due date moves later by the same number of days. With a 32-day cycle and a last period on January 5, 2026, the due date shifts 4 days to Friday, October 16, 2026.
What do early term, full term and late term mean?
ACOG defines early term as 37 weeks 0 days to 38 weeks 6 days, full term as 39 weeks 0 days to 40 weeks 6 days, late term as 41 weeks 0 days to 41 weeks 6 days, and postterm as 42 weeks or more.
When does the second trimester start?
The second trimester starts at 14 weeks 0 days and the third at 28 weeks 0 days. For a last period on January 5, 2026, the second trimester begins on April 13, 2026 and the third on July 20, 2026.
How accurate is a due date?
It is an estimate. Most babies arrive between 37 and 42 weeks, and few are born on the exact date. A first-trimester ultrasound is the most accurate way to date a pregnancy, and ACOG considers a pregnancy suboptimally dated if no ultrasound confirms or revises the due date before 22 weeks.
How we checked this page: every figure in the examples and FAQs above is produced by this calculator and verified by automated tests against known answers, and the rules and rates come from the sources below. Last updated . Spotted a problem? Tell us.