Pregnancy calculator and baby growth tracker
Find your due date and see how your baby is growing. Free, private and nothing to sign up for.
Pregnancy and baby growth at a glance
280 days
A full pregnancy counted from the first day of your last period
266 days
The same pregnancy counted from the day of conception
About 5%
Babies born on their exact due date
37–42 weeks
The range doctors call full term
12 weeks
When the first dating scan usually happens
3rd–97th
The percentile range seen in most healthy babies
Pregnancy calculator: how your due date is worked out
This pregnancy calculator gives you an estimated due date, your current week and day, your trimester and your baby’s size in one place. Pick the date you know and the pregnancy due date calculator does the rest.
Most people start with the first day of their last period. Our pregnancy due date calculator by LMP adds 280 days (40 weeks) to that date and adjusts for your cycle length if it isn’t 28 days. Once the due date is known it counts back, so it also works as a pregnancy week calculator by LMP. A pregnancy due date by LMP is the method most clinics use first, before an early scan refines it. For comparison, the NHS due date calculator uses the same last-period method.
If you know when you conceived, use the conception due date calculator, which adds 266 days. IVF transfer dates and ultrasound dates work too. Already have a due date from your doctor? Choose “I know my due date” to see how many weeks am I pregnant from my due date, in one click. The result also shows your month of pregnancy, so it doubles as a pregnancy month calculator by week.
Baby growth tracker: percentile calculators before and after birth
The second tab is a free baby growth tracker that works on any phone. If you searched for a baby growth tracker app or a baby growth tracker free download, there is nothing to install. Enter your baby’s age, weight and length and this baby growth chart calculator shows where they sit on the curve.
It works as a baby weight percentile calculator and a height and weight percentile calculator from birth to 24 months. It uses the WHO growth standards, which the CDC recommends for children under 2, so it can stand in for a CDC growth chart calculator at this age. Before birth, the baby percentile during pregnancy tool compares an ultrasound weight estimate with the typical weight for that week, from 20 to 40 weeks.
A percentile shows how your baby compares with other babies. It is not a diagnosis. A baby who keeps following the same curve is usually growing well, and your midwife or pediatrician is the right person for any worry.
What happens in each trimester
First trimester (weeks 1 to 13). The baby’s organs begin to form and the heart starts beating. This is when most people take a test, book a first appointment and get a dating scan around week 12. Use the pregnancy calculator early so you know which week you are in when you talk to your midwife.
Second trimester (weeks 14 to 27). Many people feel more energy and first movements. A detailed anomaly scan usually happens around week 20, and the baby grows from the size of a peach to the size of a head of lettuce.
Third trimester (weeks 28 to 40). Most of the baby’s weight is gained in these weeks, from about 1 kg at week 28 to around 3.4 kg by week 40. Appointments become more frequent as your due date gets closer.
How to read your baby's percentile
If your baby is on the 50th percentile, half of babies of the same age and sex weigh less and half weigh more. A baby on the 10th percentile is smaller than 90 out of 100 babies, and that can be completely healthy. One reading says much less than a pattern, so check again at each weigh-in and watch the trend.
For babies born early, use their corrected age (their age counted from the due date) until about two years. Weigh on the same scale when you can, and measure length lying flat. Percentiles change as a baby grows, and a jump between curves is a reason to ask your pediatrician, not a reason to panic.
Tips for a more accurate due date
Use the first day of full flow, not light spotting, as your last period date. If your cycle is longer or shorter than 28 days, enter your usual cycle length so the result shifts with it. If your periods are irregular or you are not sure of the date, an early ultrasound gives a better estimate than a calendar, and you can enter the scan result in the calculator. Your own doctor’s date always takes priority over any online tool.
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Frequently asked questions
Choose "I know my due date" in the Pregnancy tab. The calculator counts 40 weeks back from that date and shows today's week and day.
It is a guide, not a deadline. Only about 5% of babies arrive on the exact day, and most are born between 37 and 42 weeks. An early scan can adjust the date.
There isn't a best number. Anywhere from the 3rd to the 97th percentile is a typical range. What matters most is that your baby keeps growing along their own curve.
It adjusts for cycle length between 21 and 45 days. If your cycles vary a lot, use an ultrasound date instead, since an early scan is more reliable than a period date.