🤰 Pregnancy Due Date Calculator
Find your estimated due date using the method that fits you
Use this if you tracked ovulation or know the date you conceived.
First-trimester scans (before 14 weeks) are the most accurate for dating.
How to Operate
- Choose your method from “Calculate Based On”: Last Period (LMP), Conception Date, Ultrasound Date, or IVF Embryo Transfer.
- Pick the date from the calendar and fill in the extra field shown: your cycle length (LMP), the weeks and days on your scan (Ultrasound), or the embryo day (IVF). If you use LMP and your cycle is not 28 days, change it from the dropdown.
- Click “Calculate Due Date” to instantly see your due date, current week, and trimester.
Frequently Asked Questions
Standard calculators assume a 28-day cycle with ovulation on day 14. With a 45-day cycle, ovulation typically happens about 17 days later than that assumption (45 − 28 = 17), so your calculated due date could be off by roughly 2 to 2.5 weeks — more than most people expect. For irregular cycles, the most reliable options are: adjusting the calculation using your true average cycle length, using a tracked ovulation/conception date, or getting a first-trimester dating ultrasound, which doctors consider the gold standard for irregular cycles.
Yes. If you know your conception date, due date is calculated as 266 days (38 weeks) from conception rather than 280 days (40 weeks) from LMP. If conception date isn’t known either, a first-trimester dating ultrasound (ideally before 14 weeks) is the most accurate alternative — it’s considered more reliable than LMP-based guessing, especially for irregular cycles.
Online calculators count 280 days from your LMP, assuming a textbook 28-day cycle. An ultrasound instead measures the baby’s actual size (crown-rump length in the first trimester) to estimate gestational age directly. Medical guidelines (ACOG) recommend adjusting the due date to match the ultrasound when the two disagree by more than about 5-7 days in the first trimester, since ultrasound dating is considered more accurate — especially for irregular cycles or uncertain LMP recall.
These answers are based on in-depth research and medical guidelines, but they are not a substitute for medical advice. Please consult your doctor for guidance specific to your pregnancy.
What Is an Estimated Due Date (EDD)?
Your estimated due date is the day your baby is expected to arrive if your pregnancy lasts the standard 40 weeks. This is called an estimate for a reason. It is a planning tool for you and your healthcare provider, not a promise. It helps schedule prenatal checkups and screening tests, track your baby’s growth, and prepare for labour, delivery and life with a newborn.
One detail surprises many mothers: pregnancy is counted from the first day of your last menstrual period (LMP), not from the day you conceived. That means you are already considered about two weeks pregnant by the time conception actually happens.
How Does a Due Date Calculator Work?
Most due date calculators use a method called Naegele’s rule. It assumes a 28-day menstrual cycle with ovulation around day 14, and it adds 280 days (40 weeks) to the first day of your last period.
You can also do it by hand: take the first day of your last period, add seven days, count back three months, and move to the next year. For example, if your last period began on 10 January, adding seven days gives 17 January, counting back three months gives 17 October, and your due date would be 17 October of the same year the pregnancy ends.
If your cycles are longer or shorter than 28 days, a good calculator adjusts the result by the difference. A woman with a 32-day cycle ovulates later, so her due date shifts about four days later. If you know the date you conceived or ovulated, the calculation uses 266 days (38 weeks) from that date instead.
Due Date Calculation Methods at a Glance
Different situations call for different methods. Here is a quick comparison:
| Method | What you need | How the date is worked out | Best for |
|---|---|---|---|
| Last menstrual period (Naegele’s rule) | First day of your last period | LMP + 280 days (40 weeks) | Regular cycles of about 28 days |
| LMP with cycle adjustment | LMP and your average cycle length | 280 days, adjusted for cycles shorter or longer than 28 days | Irregular or longer/shorter cycles |
| Conception or ovulation date | Known date of conception or ovulation | Conception date + 266 days (38 weeks) | Women who track ovulation |
| IVF day-5 embryo (blastocyst) transfer | Embryo transfer date | Transfer date + 261 days | IVF with a day-5 transfer |
| IVF day-3 embryo transfer | Embryo transfer date | Transfer date + 263 days | IVF with a day-3 transfer |
| First-trimester ultrasound | Scan done by your healthcare provider | Based on the baby’s measurements at the scan | Uncertain dates or irregular cycles |
Using a Due Date Calculator After IVF
If you conceived through IVF, your clinic knows the exact age of the embryo, so the calculation is more precise. The general formula is the embryo transfer date plus 266 days, minus the number of days the embryo had developed before transfer. In practice, that means adding 261 days to a day-5 transfer and 263 days to a day-3 transfer. For instance, a day-5 transfer on 15 June gives an estimated due date of 3 March, while a day-3 transfer on the same day gives 5 March.
Can Your Due Date Change?
Yes, and it is very common. Your healthcare provider may adjust your due date after an early ultrasound, especially if your periods are irregular, you are unsure of your LMP dates, or the baby’s measurements differ noticeably from what is expected. A first-trimester ultrasound is generally the most reliable way to date a pregnancy, usually accurate to within about a week.
If your provider changes your due date, there is nothing to worry about. It simply means the new date fits your baby’s development better .Ultrasound due date calculator
How Accurate Is Your Due Date?
Only about 5% of babies are born on their exact due date. Most arrive within a couple of weeks either side of it, and the majority of babies are born between 38 and 42 weeks. Doctors use these terms to describe timing:
- Early term: 37 to 38 weeks
- Full term: 39 to 40 weeks
- Late term: 41 weeks
- Post-term: 42 weeks and beyond
Think of your due date as the middle of a window rather than a fixed deadline. First pregnancies, the length of your cycles, your health and your baby’s growth can all influence when labour begins.
Pregnancy Weeks and Trimesters
Once you know your due date, you can follow your pregnancy week by week. Pregnancy is divided into three trimesters:
- First trimester (weeks 1 to 12): Your baby’s organs begin to form. Nausea, tiredness and tender breasts are common.
- Second trimester (weeks 13 to 26): Often the most comfortable stage. Energy usually returns and you may feel your baby move for the first time.
- Third trimester (weeks 27 to 40): Your baby gains weight quickly and you prepare for birth. Aches, including hip and pelvic pain, are common as your belly grows.
Trimester boundaries vary slightly between sources, so treat these week ranges as a general guide.
What to Do After You Know Your Due Date
A few simple steps can help you make the most of your estimated due date:
- Book your first prenatal appointment. Your provider will confirm your dates and may arrange an early ultrasound.
- Write down your key dates. Note the first day of your last period, your cycle length and your due date so you have them handy at appointments.
- Plan your checkups and tests. Many screenings and scans are scheduled by pregnancy week, so an accurate date matters.
- Look after your health. Eat well, rest, stay hydrated and take any supplements your doctor recommends. Gentle exercise such as walking or prenatal yoga can also help you feel stronger and more comfortable, if your doctor says it is safe for you.
- Prepare gradually. Use your due date to plan maternity leave, set up your hospital bag and arrange support for after the birth.
Final Thoughts
A pregnancy due date calculator is a quick, helpful starting point, but your due date remains an estimate. Use it to plan ahead, stay flexible, and let your healthcare provider confirm your dates with an ultrasound. When you are ready, enter your details in the calculator above to get your estimated due date and see how far along you are.
This article is for general information only and is not a substitute for professional medical advice. Always speak to your doctor or midwife about your pregnancy.Choose the one that fits you IVF due date calculator
Trying to conceive? Find your fertile days with the ovulation calculator.