Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period or your conception date — and see your current gestational age and trimester.
From the first day of your last period
Today's date is taken from your device clock. Estimates only — your midwife or doctor will use the dating scan as the official due date once it's available.
Formula
Two short formulas — pick the tab for what you have:
- From LMP:
due date = LMP + 280 days + (cycle length − 28). The cycle adjustment shifts ovulation, and so the due date, by the same number of days. - From conception:
due date = conception + 266 days.
Trimesters use the standard clinical boundaries: trimester 1 ends at 14 weeks 0 days, trimester 2 at 28 weeks 0 days, and trimester 3 runs from there to the due date.
When this calculator helps
This calculator works out an estimated due date from the first day of your last menstrual period using Naegele's rule, the method used across European antenatal services. It adds 280 days — 40 weeks — to that first day, which is how a full-term pregnancy is counted from the start of your last period rather than from conception. It is the simplest way to get an early sense of when your baby might arrive as soon as you have a positive test.
Treat it as a planning estimate rather than an exact prediction. A rough due date helps you think about when to arrange your first antenatal appointment, when maternity leave might begin, and how the coming months are likely to unfold. But it is only an estimate: just around 4% of babies arrive on the exact date the rule gives, so read the result as the centre of a range rather than a fixed day.
How to read your result
The date shown is your estimated due date — the point at which you would be 40 weeks pregnant counting from your last period. Around it sits the term window most European guidelines and the WHO use: birth before 37 weeks is considered preterm and after 42 weeks post-term, so a healthy arrival anywhere across roughly 37 to 42 weeks is entirely normal.
The result also shows which trimester you are in. The first trimester runs from your last period to the end of week 13, the second from week 14 to week 27, and the third from week 28 until birth. These boundaries are clinical conventions shared across European antenatal care rather than biological switches, but they are a useful way to track which stage — and which scans and checks — you have reached.
A worked example
Suppose the first day of your last period was 01/02/2026 and you have a typical 28-day cycle. Adding 280 days gives an estimated due date of 08/11/2026. If today were 01/06/2026, you would be about 17 weeks pregnant — well into the second trimester, with the anatomy scan around 20 weeks still ahead. Move the start date a week earlier and the whole window shifts earlier too, which is why getting that first date right is worthwhile.
Common mistakes to avoid
A few simple misunderstandings can move the estimate by days or weeks, so it is worth checking these before you depend on the figure.
- Assuming a 28-day cycle when yours is reliably longer or shorter — every day over 28 pushes the due date a day later, so enter your real cycle length.
- Treating the due date as fixed; it is the centre of a 37-to-42-week term window, not a guaranteed day of birth.
- Confusing gestational age (counted from your last period) with fetal age (counted from conception, about two weeks less) — pregnancy weeks are quoted as gestational age.
- Relying on an uncertain memory of your last period when an early dating scan would give a far more reliable starting point.
How this fits maternity care across Europe
Maternity care and scan schedules vary from one European country to the next, so your LMP-based estimate is only a starting point. Most services confirm and refine the date with a first-trimester dating scan, often somewhere between 11 and 14 weeks, followed by an anatomy scan around 20 weeks. If the dating scan disagrees with your last-period date by more than about a week, the scan date is generally given priority.
Because the details differ by country, always follow the due date your local midwife, GP, or gynaecologist confirms. This calculator is informational only and does not replace antenatal care — use it for orientation, and take any questions or concerns about your pregnancy to your own care provider.
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Frequently asked questions
How is the due date calculated?▾
The standard formula is Naegele's rule: first day of last menstrual period (LMP) plus 280 days, or 40 weeks. The rule assumes a 28-day cycle with ovulation on day 14. Most European antenatal services use this calculation when first contacting a pregnant person, then refine it using a first-trimester dating scan (typically between 11 and 14 weeks). If the scan and LMP disagree by more than about a week, scan dating is given priority.
What if my cycle is shorter or longer than 28 days?▾
Adjust the cycle length input — each day longer than 28 shifts the estimated due date one day later, because ovulation (and so conception) is later. The calculator uses (cycle length − 28) as the adjustment. For very irregular cycles, scan dating is more reliable than LMP-based dating, and that's what your midwife or gynaecologist will use to set the official due date.
Will the baby actually be born on the due date?▾
Most babies don't arrive on the exact due date — only around 4% do. The full-term window is roughly 37 to 42 weeks; the WHO and most European obstetric guidelines treat birth before 37 weeks as preterm and after 42 weeks as post-term. Induction policies vary by country, but most maternity services discuss induction between 41 and 42 weeks if labour hasn't started spontaneously.
When does each trimester start and end?▾
Trimester 1 covers weeks 0–13, trimester 2 weeks 14–27, and trimester 3 from week 28 to birth. These boundaries are clinical conventions used across European antenatal services. Key milestones include the first appointment with a midwife/doctor (usually 8–12 weeks), the dating scan (11–14 weeks), the anatomy scan (around 20 weeks), and group B strep screening or third-trimester growth checks later in the pregnancy depending on country.
When should I contact a midwife or doctor?▾
European countries vary, but most antenatal systems recommend contacting a midwife, GP, or gynaecologist in the first trimester — typically between 6 and 10 weeks. The first appointment confirms the pregnancy, takes your history, arranges blood tests and the dating scan, and starts the antenatal care schedule. Earlier contact is useful if you have any pre-existing health conditions, take regular medication, or are unsure about cycle dates.