Pregnancy tool
Due date calculator
Estimate your baby’s due date, how many weeks pregnant you are today and which trimester you are in — from your last period, a conception date or a dating scan. Everything is worked out privately in your browser.
Enter a date and press Calculate to see your estimated due date and how far along you are.
Educational estimate only. This is not a diagnosis or a substitute for antenatal care. A dating scan from your maternity team is more accurate than a calculation — always follow the due date and advice they give you.
What your due date does and doesn’t mean
A due date is a single day picked out of a normal range. A pregnancy is counted as term anywhere from 37 to 42 weeks, and only about 1 baby in 20 arrives on the estimated day itself. Think of it as the middle of a likely window, not a deadline.
In the UK, gestational age is counted from the first day of your last period, not from conception — which is why you are already counted as “two weeks pregnant” at conception. Pregnancy is divided into three trimesters:
- First trimester — week 1 to the end of week 12
- Second trimester — week 13 to the end of week 26
- Third trimester — week 27 until birth
Book with a midwife or GP as early as you can — ideally before 10 weeks — so your first scan and antenatal care can be arranged. Explore our pregnancy & baby hub for what to expect in each trimester and the warning signs that always need urgent checking.
Answers
Due date calculator: frequently asked questions
How is a due date worked out?
The standard estimate (Naégele’s rule) counts 280 days — 40 weeks — from the first day of your last menstrual period (LMP), assuming a regular 28-day cycle. If your cycle is longer or shorter, the estimate shifts by the difference. From a conception or ovulation date, it counts 266 days. Only about 1 in 20 babies actually arrive on the exact due date — anywhere from 37 to 42 weeks is considered term.
Is the last-period method or a scan more accurate?
A dating scan (usually at 11–14 weeks in the UK) is more accurate than the last-period date, especially if your cycle is irregular or you are unsure of dates. If your scan gives a different due date, use the scan date — that is what your maternity team will use.
What is gestational age?
Gestational age is how far along the pregnancy is, counted in weeks and days from the first day of your last period — not from conception. Because of this convention, you are counted as “2 weeks pregnant” around the time of conception. The calculator shows your gestational age and which trimester it falls in.
Does this replace antenatal care?
No. This is an educational estimate only. Book with a midwife or GP as early as possible in pregnancy (ideally before 10 weeks in the UK) so your care and scans can be arranged. Always follow the dates and advice your maternity team give you.
Understand each stage of pregnancy
Plain-English, clinically reviewed guides to pregnancy, common symptoms and when to get help.