Pregnancy Calculator: Know Your Estimated Due Date

A Pregnancy Due Date Calculator picks the first day of your last menstrual period (LMP) as a starting point to calculate when you can expect your little one’s arrival. Working on the assumption that a normal pregnancy lasts around 40 weeks, or 280 days, this calculator estimates your due date by adding this duration from your last period’s start date.

Some calculators might also ask how long your cycle usually is. This can make the estimate a bit more accurate, especially if your cycles are a lot shorter or longer than average. If you happen to know when you conceived or have had an early ultrasound, that can help make the prediction more precise, too. Just bear in mind, the due date calculator is only giving an educated guess - every pregnancy progresses differently, and babies often show up a few days early or late to the party.

There are many ways to calculate your due date. If you happen to know the exact day you conceived, your due date can be 38 weeks from that day.

It's generally difficult to remember the day you conceived. Even if you had sex just once or twice during your fertile window, conception may happen 2-4 days later because sperm can live up to five days in the body.

So, how exactly can you know the day you conceived? How do you calculate your due date? Read along to learn how!

1: First Day Of Your Last Period

You can calculate your due date using the first day of your last period. Counting 40 weeks from the first day of your last menstrual period (LMP) can help. Doctors also use this method to calculate the due date before the first ultrasound. (You can even choose "Last Menstrual Period" from the tools menu above to calculate.)

Women typically ovulate 2 weeks after their menstrual cycle, which is when their fertile window also starts, making it easier to calculate the due date based on the last menstrual cycle.

For example, if you have an average menstrual cycle length (28-day cycle), your period probably started 2 weeks before you conceived. This is why most pregnancies last 40 weeks instead of 38 weeks.

If you remember the first day of your last menstrual period, you can use our pregnancy due date calculator to determine your estimated due date.

2: Last Menstrual Period (LMP)

Your last menstrual period is one of the most commonly used methods to estimate pregnancy due date. It works on a simple principle: pregnancy is counted as 40 weeks (or 280 days) from the first day of your last menstrual period. This method is widely used because most women can recall their last period date more easily than the exact date of ovulation.

When you enter the first day of your last period, the calculator gives you an estimated due date. It also helps to track important pregnancy milestones, such as trimester changes and scan timelines. And while it’s a reliable starting point, the date is still an estimate. That’s because only about 5% of babies are born exactly on their due date.

3: Conception Date

The conception date method estimates your pregnancy due date by counting 38 weeks (or 266 days) from the day conception occurred (supposedly). This method can feel more intuitive, especially for women who have tracked ovulation closely, undergone fertility treatments, or have a fairly clear idea of when conception happened.

By entering the approximate conception date, the calculator projects an expected delivery date. However, it’s important to remember that pinpointing the exact day of conception isn’t always easy. That’s because sperm can survive in the body for up to five days, and ovulation timing can vary, which may slightly affect accuracy.

4: IVF Transfer Date Method

If you have conceived through IVF, calculating your due date is easier and more precise than natural conception. That is because you know the exact date of embryo transfer.

Here is how it works: For a Day 3 embryo transfer, add 263 days to your transfer date. For a Day 5 embryo transfer, add 261 days to your transfer date. You add fewer days for a Day 5 embryo transfer because it's already been growing for 5 days, while a Day 3 embryo has only been growing for 3 days. This calculation makes IVF due dates more accurate than natural pregnancy estimated due dates, as the fertilisation timing is known precisely.

Your fertility clinic will confirm this with an early ultrasound between 8 and 12 weeks, but the transfer date method gives you a reliable starting point. Most IVF due date calculators only need two things: your transfer date and whether it was a Day 3 or Day 5 embryo.

5: Ultrasound Scan

An ultrasound scan is a trusted method for determining your due date. This is especially useful when you cannot recall your last period date or for those who have irregular periods. Early ultrasounds, usually taken in the first trimester, estimate the due date accurately as they calculate it by measuring the size of the fetus. Your doctor measures the baby during the scan and compares it with standard growth charts to calculate your due date. Most women get an ultrasound between 8 and 13 weeks of pregnancy to get their due date. Your doctor will use this ultrasound date as your official due date.

Estimating your due date helps you and your doctor plan your pregnancy, but it’s important to understand that it’s an approximate timeline, not a fixed deadline. The date you’re given simply predicts when your baby is most likely to arrive, not the exact day labor will begin. Many natural factors can influence when delivery actually happens.

The reliability of a due date depends on how it’s calculated and your individual cycle. The commonly used Last Menstrual Period (LMP) method assumes a regular 28-day cycle with ovulation around day 14, which isn’t true for everyone. If your cycles are shorter, longer, or irregular, or if ovulation occurs earlier or later, the estimated date may shift. Individual circumstances also matter—pregnancies conceived through IVF or dated using early ultrasounds are usually more accurate because they rely on clearly defined events.

Overall, while a due date can’t predict the exact date, it remains a helpful planning guide. Most babies arrive one to two weeks either side of their due date, with only about 5% born on the predicted day.

Yes, due dates can change during pregnancy. These dates indicate a timeframe rather than a fixed deadline. An ultrasound in the first trimester can sometimes provide an approximate estimate, as it shows the baby’s size and stage of development. Doctors may adjust the due date when these measurements don't align with the original calculation.

As the pregnancy continues, natural variations in how each baby grows can also influence expectations around timing.

If you already know your due date, our pregnancy calculator can be beneficial. You can use the calculator to determine the timeline of your pregnancy by just entering your known due date. The calculator is programmed to provide a detailed pregnancy timeline and highlight all your important milestones, expected symptoms, etc. Apart from briefing you about the milestone, you can also check when you may be due for your prenatal tests and visits.

The calculator is a useful tool for all expectant mothers and their partners to get most answers related to their pregnancy milestones. It is important to keep in mind that your due date is just an estimate and can change.

Congratulations! You got a positive pregnancy test result! Whether you feel joy, anxiety, fear, or a mix of emotions, remember that all these feelings are completely normal - and you are not alone in this journey. Take a deep breath and remember - you don’t have to figure out everything immediately. Your first step should be to schedule an appointment with your gynaecologist, typically between 6 and 8 weeks of your last menstrual period. Although the pregnancy tests done today yield highly accurate results with more than 98% accuracy, getting the same confirmation from a doctor is better. Meanwhile, you can start eating healthy, keep yourself hydrated and rest well. It is natural to be overwhelmed, but do keep in mind that you have your family, friends and healthcare professionals to support you in your pregnancy journey.

The best time to take a pregnancy test is after your period is missed, as this allows the pregnancy hormone hCG to rise to detectable levels and reduces the chance of a false negative. Knowing when you ovulated can help you estimate when your period was due, since menstrual bleeding usually begins about 14 days after ovulation. You can track ovulation using ovulation predictor kits or by monitoring your basal body temperature.

If you don’t want to wait for a missed period, early pregnancy tests can be taken a few days beforehand, but their accuracy is higher if conception happened earlier in your cycle. If you’ve undergone fertility treatment or received an hCG trigger shot, it’s best to wait two weeks before testing, as doing so too soon may give misleading results. For the most accurate reading, take the test first thing in the morning, when urine is most concentrated.