Four dating methods, one page
Last period, conception or ovulation date, IVF transfer day and ultrasound-based dating — switch between them and compare without reloading or hunting for another tool.
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Due Date Calculator — Find Your Baby’s Due Date
Estimate your delivery date from your last period, conception date, IVF transfer or an ultrasound scan — then see exactly how many weeks pregnant you are today, which trimester you’re in and every milestone ahead on one clean timeline.
4 calculation methods
Irregular cycles supported
Full pregnancy timeline
Nothing stored or shared
Calculate your due date
Pick the method that matches the information you have. Everything runs in your browser — no data leaves this page.
Your results will appear here
Enter a date on the left and we’ll map out your due date, current week, trimester and full milestone schedule.
Why this calculator
Built to answer the questions other due date calculators skip
Most pregnancy due date calculators return a single date and stop there. This one shows the maths, adapts to your cycle and lays out the whole 40 weeks.
Adjusts for irregular cycles
Naegele’s rule assumes a textbook 28-day cycle. Set yours anywhere from 20 to 45 days and the estimate shifts with your real ovulation day instead of a default.
Complete milestone timeline
Dated checkpoints for the anatomy scan, glucose test, viability, early term and full term — with everything you have already passed marked off automatically.
Trimester dates, not just numbers
See the exact calendar window for each trimester so you can plan leave, travel cut-offs and appointments around real dates.
Completely private
Every calculation happens in your browser. No account, no email, nothing about your pregnancy is uploaded, stored or passed to a third party.
Fast and mobile-first
No heavy scripts, no pop-ups and no ad clutter. It loads in a moment and works one-handed on a phone at the clinic.
How to use it
How to calculate your due date in four steps
Choose your method
Last period is the usual starting point. Use conception, IVF or ultrasound if you have a more precise date.
Enter your date
For the LMP method, use the first day of bleeding — not the day it ended or the day you tested positive.
Set your cycle length
If your cycles run longer or shorter than 28 days, change it. This alone can move a due date by several days.
Read your timeline
Get the due date, how far along you are today, your trimester windows and every upcoming milestone with dates.
Benefits
What knowing your due date actually gives you
An estimated due date (EDD) is the anchor for almost every decision in pregnancy care — which is why getting it right, and understanding its margin of error, matters.
Time your scans and tests correctly
Nuchal translucency, the anatomy scan and the glucose test all have narrow windows tied to gestational age.
Plan maternity leave with real dates
Notice periods and leave start dates are far easier to file when you can see the calendar week by week.
Know your travel cut-offs
Most airlines restrict flying from around 36 weeks, and many require a letter after 28 weeks.
Track growth and development
Every week-by-week guide is written against gestational age, so the right week means the right information.
Understand preterm and post-term
Before 37 weeks is preterm; after 42 weeks is post-term. Both change how your care team manages the birth.
Set realistic expectations
Only a small share of babies arrive on the estimated date. A due window is more useful than a single day.
The method
How due dates are calculated
The 280-day rule (Naegele’s rule)
A standard pregnancy is dated as 280 days — 40 weeks — from the first day of your last menstrual period. That is roughly two weeks before you actually conceived, which is why you are counted as “4 weeks pregnant” around the time a test first turns positive. The classic shortcut is to take the first day of your last period, subtract three months and add seven days.
Why cycle length changes the answer
Naegele’s rule assumes ovulation on day 14 of a 28-day cycle. If your cycles run 32 days, you usually ovulate around four days later, so the due date moves about four days later too. This calculator applies that correction automatically instead of pretending every cycle is identical.
Dating from conception, IVF and ultrasound
If you know the conception or ovulation date, the due date is 266 days from it. IVF is the most exact of all because the embryo age is known: a day-5 blastocyst transfer is dated 261 days from transfer, a day-3 transfer 263 days. An early ultrasound measures the embryo directly, and if that measurement disagrees with your LMP date by more than about five to seven days in the first trimester, clinicians will normally re-date the pregnancy to the scan.
The 40 weeks at a glance
| Stage | Gestational age | What it marks |
|---|---|---|
| First trimester | 0 – 13 weeks 6 days | Organ formation, first prenatal visit, dating scan |
| Second trimester | 14 – 27 weeks 6 days | Anatomy scan around week 20, first movements |
| Third trimester | 28 weeks to birth | Rapid growth, more frequent appointments |
| Early term | 37 – 38 weeks 6 days | Birth is no longer considered preterm |
| Full term | 39 – 40 weeks 6 days | Optimal window for delivery |
| Late and post-term | 41 weeks and beyond | Monitoring increases; induction may be discussed |
How accurate is an estimated due date?
It is an estimate, not an appointment. Roughly one baby in twenty arrives on the estimated date itself, while the large majority are born in the two weeks either side of it. First-trimester ultrasound dating is the most reliable method available; accuracy falls as pregnancy progresses because babies grow at increasingly different rates. Treat your EDD as the centre of a window rather than a deadline.
FAQ
Due date calculator questions, answered
How do I calculate my due date from my last period?
Add 280 days (40 weeks) to the first day of your last menstrual period. The shortcut version is to subtract three months from that date and add seven days. If your cycle is not 28 days long, add or subtract the difference — a 31-day cycle pushes the due date about three days later. This calculator does that adjustment for you.
How many weeks pregnant am I right now?
Your current gestational age is the number of days between the first day of your last period and today, expressed in weeks and days. Because dating starts from your last period rather than conception, you are counted as about two weeks pregnant at the moment you conceive. Enter your date above and the tool shows your exact week and day, updated to today.
Can I calculate a due date if my periods are irregular?
Yes, but with a wider margin of error. If you can estimate an average cycle length, set it in the tool for a better result. With very irregular cycles the most reliable route is an early ultrasound, ideally before 14 weeks, which dates the pregnancy from the baby’s measurements rather than your calendar.
How is an IVF due date different?
IVF dating is the most precise because the embryo’s exact age is known. A day-5 blastocyst transfer is dated 261 days from the transfer date, a day-3 transfer 263 days, and an egg retrieval date 266 days. There is no cycle-length guesswork involved, so the estimate does not shift the way an LMP-based date can.
Why did my doctor change my due date after the scan?
If a first-trimester ultrasound disagrees with your period-based date by more than roughly five to seven days, most guidelines recommend re-dating the pregnancy to the scan, because early measurements are more reliable than recall of a period date or an assumed ovulation day. Later scans are used to check growth rather than to re-date.
What are the chances of giving birth on my due date?
Low — only about one in twenty births happens on the estimated date. The vast majority of babies arrive between 37 and 42 weeks. It helps to think of your due date as the middle of a several-week window and to have plans ready a couple of weeks either side.
Can I work out my conception date from my due date?
Yes. Subtract 266 days from the estimated due date to get the approximate conception or ovulation date. Bear in mind sperm can survive several days in the reproductive tract, so the date of conception and the date of intercourse are not always the same day. The tool shows your estimated conception date alongside the result.
Get your due date and full pregnancy timeline in seconds
Free, private and accurate to the day — with the milestones, trimester windows and week-by-week countdown that most calculators leave out.
This due date calculator provides general estimates for planning and information only. It is not medical advice and cannot replace an assessment by a qualified healthcare professional. Always confirm your due date and any decisions about your care with your midwife, obstetrician or doctor.