Productive ToolboxPregnancy Due Date Calculator
Estimate your due date from your last period, conception date, IVF transfer or an ultrasound, and see how far along you are.
28 days is typical; a longer cycle moves the due date later
An estimate only. Your doctor or midwife will confirm the due date, usually with an early ultrasound.
Choose a date to see your due date.
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How Your Due Date Is Estimated
Doctors and midwives date a pregnancy from the first day of the last menstrual period (LMP), because that date is usually known while conception is not. A typical pregnancy lasts 40 weeks from the LMP, which is about 38 weeks from conception.
Due date (LMP) = LMP + 280 days + (cycle length − 28)
Due date (conception) = Conception + 266 days
Due date (IVF) = Transfer date + 266 − embryo age in days
Weeks pregnant = (Today − LMP) ÷ 7
Example: a last period starting on January 1, 2026 with a 28-day cycle gives a due date of October 8, 2026.
Pregnancy Trimesters and Milestones
| Stage | Weeks |
|---|---|
| First trimester | 0 – 13 weeks 6 days |
| Second trimester | 14 – 27 weeks 6 days |
| Third trimester | 28 weeks until birth |
| Preterm | Before 37 weeks |
| Early term | 37 weeks 0 days – 38 weeks 6 days |
| Full term | 39 weeks 0 days – 40 weeks 6 days |
| Late term | 41 weeks 0 days – 41 weeks 6 days |
| Post-term | 42 weeks and later |
Term definitions from the American College of Obstetricians and Gynecologists (ACOG).
How to Use the Due Date Calculator
- 1Choose how to calculate: Pick last period if you know the first day of your last menstrual period, or conception date, IVF transfer date or an ultrasound result if you have one.
- 2Enter the date: Choose the first day of your last period, the conception or transfer date, or the date of the scan.
- 3Add the details: For last period, enter your usual cycle length; for IVF, whether the embryo was transferred on day 3 or day 5; for an ultrasound, the gestational age the scan gave.
- 4Read your due date: See the estimated due date, how many weeks and days pregnant you are today, your trimester, and dates such as the end of the first trimester and full term.
Frequently Asked Questions
How is the due date calculated?
With Naegele's rule: 280 days (40 weeks) after the first day of your last menstrual period, assuming a 28-day cycle. A last period that started on January 1 gives a due date of October 8. From a known conception date, the due date is 266 days (38 weeks) later.
What if my cycle is longer or shorter than 28 days?
Ovulation usually happens about 14 days before the next period, so a longer cycle means later ovulation and a later due date. The calculator moves the due date by the difference: with a 32-day cycle, it is 4 days later than with a 28-day cycle.
How is the due date worked out after IVF?
From the transfer date: 266 days after conception, where a day-5 blastocyst transfer counts as conception 5 days earlier, so the due date is 261 days after a day-5 transfer and 263 days after a day-3 transfer.
Why are pregnancy weeks counted from the last period?
Because the start of the last period is usually known and conception is not. By this convention you are already about 2 weeks pregnant at conception, which is why a pregnancy is called 40 weeks long although the baby develops for about 38.
How accurate is the due date?
It is an estimate: only about 4–5% of babies arrive on their due date, and most are born within two weeks either side of it. A first-trimester ultrasound, measured from the baby's crown-rump length, is the most accurate way to date a pregnancy, so your provider may adjust the date after it.
What do early term, full term and late term mean?
Babies born from 37 weeks 0 days to 38 weeks 6 days are early term, 39 weeks 0 days to 40 weeks 6 days full term, 41 weeks late term and from 42 weeks post-term (ACOG definitions). Before 37 weeks a birth is preterm.
Is my information private?
Yes. The calculation runs in your browser and the dates you enter are not sent or stored anywhere.
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