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.
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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.