More than a due date: your pregnancy milestone calendar
Most people looking for a pregnancy due date calculator want to plan ahead — when will the first trimester end, when is the anatomy scan likely, when does the baby count as full term? This calculator answers all of those at once. Enter any one of four dates and it builds a table of the milestones that matter, all worked out from the same estimated due date.
The milestones are counted in completed weeks from the first day of your last period (gestational age), the same way your prenatal care team counts them:
| Milestone | Gestational age | Days after LMP |
|---|---|---|
| Missed period / positive test usually possible | about 4 weeks | 28 |
| End of first trimester | 13 weeks 6 days | 97 |
| Common anatomy-scan window | 18–22 weeks | 126–154 |
| Third trimester begins | 28 weeks | 196 |
| Early term | 37 weeks | 259 |
| Full term | 39 weeks | 273 |
| Estimated due date | 40 weeks | 280 |
| Late term | 41 weeks | 287 |
| Post-term | 42 weeks | 294 |
Four ways to enter your dates
- Last period — the standard method. The due date is 280 days after the first day of your last period, adjusted for your cycle length.
- Conception date — adds 266 days to the date you conceived.
- IVF transfer — adds 266 days minus the age of the embryo (263 days for day-3, 261 for day-5 and 260 for day-6 embryos).
- Ultrasound — if a scan told you how far along you were on a given day, the calculator projects forward from that measurement. Scans in the first trimester are generally the most reliable for dating.
Because every method converts your date into the same 40-week scale, the milestones line up whichever method you use. If two methods give you different answers, use the date your healthcare professional has confirmed.
What full term really means
“Full term” has a specific meaning. Professional bodies such as the American College of Obstetricians and Gynecologists divide the end of pregnancy into early term (37 weeks 0 days to 38 weeks 6 days), full term (39 weeks 0 days to 40 weeks 6 days), late term (41 weeks 0 days to 41 weeks 6 days) and post-term (42 weeks onward). Your due date sits in the middle of the full-term window, which is why it is better to plan around that two-week range than a single day.
How the pregnancy due date is worked out for each method
Whichever date you enter, the calculator first converts it into the same reference point — the equivalent first day of your last period — and then adds 280 days:
| You enter | Due date formula | Example |
|---|---|---|
| First day of last period | + 280 days (± cycle adjustment) | Jan 10 → Oct 17 |
| Conception date | + 266 days | Jan 24 → Oct 17 |
| Day-5 IVF transfer | + 261 days | Jan 29 → Oct 17 |
| Ultrasound at 8 weeks 0 days | scan date + (280 − 56) days | Mar 7 → Oct 17 |
All four examples describe the same pregnancy, which is why the results line up (dates shown for a non-leap year). If the methods you try give different answers for your own pregnancy, that is useful information to share with your midwife or doctor at your first appointment.
Your pregnancy month by month
Pregnancies are tracked in weeks, but many people think in months. This overview pairs each month with the weeks it covers and the things that commonly happen then — use the milestone table in your result for your own dates.
| Month | Weeks | Common milestones |
|---|---|---|
| 1 | 1–4 | Ovulation, conception and implantation; a home test may turn positive around the missed period |
| 2 | 5–8 | Early symptoms; first prenatal appointment often booked |
| 3 | 9–13 | Dating scan and first-trimester screening options; end of the first trimester |
| 4 | 14–17 | Second trimester begins; second-trimester screening may be offered |
| 5 | 18–22 | Anatomy scan; first movements often felt |
| 6 | 23–27 | Glucose screening window opens at 24 weeks |
| 7 | 28–31 | Third trimester begins; appointments usually become more frequent |
| 8 | 32–35 | Birth planning; baby often settles head-down |
| 9 | 36–40+ | Group B strep screening, weekly visits, early term from 37 weeks and full term from 39 weeks |
For a week-by-week version with your actual dates, open the Pregnancy Timeline, or read about a specific week such as 20 weeks pregnant.
A practical checklist for each trimester
First trimester
- Book your first prenatal appointment and ask how your due date will be confirmed.
- Ask about first-trimester screening options and when they are available.
- Note the end-of-first-trimester date from your result if you plan to share your news after it.
Second trimester
- Put the anatomy-scan window (18–22 weeks) in your calendar.
- Ask when glucose screening is planned — commonly between 24 and 28 weeks.
- Start planning parental leave: count working days with the Days Between Dates calculator.
Third trimester
- Discuss your birth preferences and how to reach your care team when labour starts.
- Prepare a hospital or birth bag a few weeks before the early-term date (37 weeks).
- Remember that birth anywhere from 37 to 42 weeks is within the normal range — plan for the whole window.
Irregular periods and the pregnancy due date
If your cycles vary a lot, the first day of your last period is a less reliable starting point, because ovulation may have happened well before or after day 14. In that case, enter your best estimate, set the cycle length to your typical average, and treat the result as provisional. A conception or ovulation date (if you tracked it) usually gives a better estimate, and an early ultrasound will normally set the official due date. The same applies if you conceived soon after stopping hormonal contraception or while breastfeeding, when cycles are often irregular.
Twins and multiples
The pregnancy due date for twins or triplets is calculated in exactly the same way — the 40-week point does not change. In practice, multiple pregnancies are more likely to be delivered before the due date, and care teams usually plan extra scans and appointments. The milestone dates in your result are still useful as reference points; your care team will explain the timing that applies to your pregnancy. For IVF twins, use the IVF Due Date Calculator with your transfer date.
Why pregnancy is “40 weeks” and not “9 months”
A pregnancy due date is 280 days after the first day of the last period. Because calendar months average about 30.4 days, 280 days is a little over nine months — roughly nine months and one week. Counting in months is also ambiguous (is the first month the one with your last period, or the one when you conceived?), which is why care teams use weeks and days. Remember too that the first two of those 40 weeks happen before conception: on the day you conceive, you are already counted as two weeks pregnant.
First pregnancy vs. later pregnancies
The same 280-day rule is used for every pregnancy, but individual pregnancies vary in length. On average, first pregnancies tend to last slightly longer than later ones, and some people find their pregnancies follow a similar pattern each time. That does not change your estimated due date — it is simply another reason to treat the due date as the centre of a window. If you had a previous pregnancy, you can enter its dates in the calculator to see how its length compared.
Leap years, holidays and other date details
The calculator counts real calendar days, so a pregnancy that runs through February 29 is handled automatically — the due date may be one day different from a non-leap-year calculation done by hand. A due date that falls on a public holiday or weekend is no more or less likely to be the birth day than any other date. If you want to know how many working days remain before the due date (for example to plan leave), use the Days Between Dates calculator, which also counts weekdays.
Saving and sharing your pregnancy dates
Every result can be copied, shared as a link or printed. The share link contains the date you entered so the same result opens for the person you send it to — share it only with people you trust. Nothing you type is stored on our servers. Printing gives you a one-page summary with your due date, current week and milestone dates to bring to your first appointment.
Due date vs. actual birth date
Your pregnancy due date is a midpoint, not a promise. Only a small share of babies — often quoted at around 4–5% — arrive on the due date itself, while most are born within about two weeks either side. Some babies come earlier than 37 weeks (preterm), which is one reason regular prenatal care matters. If you have any signs that worry you at any stage, contact your midwife, doctor or maternity unit rather than waiting for your due date.
Planning with your pregnancy calendar
Use the milestone dates to plan practical things: telling family and friends after the first trimester, booking a scan, arranging parental leave or preparing for the birth. To count working days until your leave starts, use the Days Between Dates calculator; to see each week laid out on the calendar, open the Pregnancy Timeline. The original Due Date Calculator explains the formulas in depth.