Precision Utility
Due Date
Calculator
Method
Naegele's Rule
Tracking
Trimester
Find out when your baby is due in seconds. Enter the first day of your last menstrual period and your cycle length — the calculator estimates your due date using Naegele's rule, shows your current trimester, weeks pregnant and key pregnancy milestones.
Pregnancy Parameters
Estimated Due Date
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Due Date
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Weeks Pregnant
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Trimester
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Days Remaining
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Trimester Progress
Enter your LMP date to see progress
Key Milestones
Important dates throughout your pregnancy
1st Trimester Ends
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Week 12
Viability
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Week 24
2nd Trimester Ends
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Week 27
3rd Trimester
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Week 28
Full Term
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Week 37
Due Date
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Week 40
How the due date calculator works
Start by entering the first day of your last menstrual period (LMP). This is the date doctors use as the starting point for calculating gestational age, even though conception typically happens around two weeks later.
Next, set your average cycle length. The standard is 28 days, but cycles anywhere from 20 to 45 days are normal. If your cycle is longer or shorter than 28 days, the calculator adjusts the due date accordingly.
Hit calculate and you'll see your estimated due date, how many weeks pregnant you are today, which trimester you're in and how many days remain until your due date. The trimester progress bar shows exactly where you are in your pregnancy at a glance.
Scroll down to see six key milestones — from the end of the first trimester at week 12 through to full term at week 37 and your due date at week 40.
What you need to know about due dates
This calculator uses Naegele's rule, the same method used by midwives and GPs as a first estimate. It takes your LMP date, adds 280 days (40 weeks) and adjusts for your cycle length. If your cycle is 32 days instead of 28, your due date shifts 4 days later.
Cycle length matters. Ovulation doesn't always happen on day 14. Women with longer cycles tend to ovulate later, which means conception — and therefore the due date — is pushed back. Entering your actual cycle length gives a more accurate estimate.
Pregnancy is divided into three trimesters. The first trimester (weeks 1–12) covers early development. The second trimester (weeks 13–27) is often when symptoms ease and movement is first felt. The third trimester (weeks 28–40) is the final stretch before birth.
Your NHS booking appointment is usually around 8–10 weeks. At this visit your midwife will take your medical history, arrange blood tests and book your dating scan. The dating scan at 8–14 weeks uses ultrasound measurements to confirm or adjust your due date.
Only about 4% of babies are born on their exact due date. Most arrive within two weeks either side. A pregnancy is considered full term from 37 weeks, and post-term after 42 weeks, when induction is usually offered.
Frequently asked questions
How is my due date calculated?
Your due date is calculated using Naegele's rule: take the first day of your last menstrual period (LMP), add 280 days (40 weeks), then adjust for your cycle length if it differs from the standard 28 days.
What if my cycle is longer or shorter than 28 days?
The calculator adjusts automatically. If your cycle is longer than 28 days, your due date shifts later by the same number of extra days. A shorter cycle brings it earlier. For example, a 32-day cycle adds 4 days to the standard estimate.
How accurate is the estimated due date?
Only about 4% of babies are born on their exact due date. Most arrive within two weeks either side. An NHS dating scan at 8–14 weeks gives a more precise estimate based on the baby's measurements.
What are the three trimesters of pregnancy?
The first trimester runs from week 1 to week 12, the second from week 13 to week 27, and the third from week 28 until birth (typically week 40). Each trimester brings different developmental milestones for the baby.
When should I book my first NHS midwife appointment?
Contact your GP or midwife as soon as you know you're pregnant. Your booking appointment is usually around 8–10 weeks. The NHS dating scan is offered between 8 and 14 weeks to confirm your due date.
What does 'full term' mean?
A pregnancy is considered full term from 37 weeks. Babies born between 37 and 42 weeks are classed as term births. Before 37 weeks is preterm, and after 42 weeks is post-term, at which point induction is usually offered.