Baby Due Date Countdown

Standard pregnancy is 280 days (40 weeks) from the first day of last menstrual period (LMP) - or about 38 weeks from actual conception. Naegele's rule: due date = LMP date + 9 months + 7 days, or LMP + 280 days. So an LMP of 1 January gives a due date of approximately 8 October. Most due date calculators use this method.

Only about 4-5% of babies arrive on the actual due date. Most arrive within 2 weeks either way - 'term' pregnancy is 37-42 weeks. First-time mothers tend to deliver slightly later (averaging 8 days past LMP-based due date). Repeat mothers tend to be closer to or slightly before. Healthcare professionals use LMP for the original due date but adjust based on early ultrasound (6-13 weeks) which is generally more accurate than LMP for women with irregular cycles.

First trimester (1-13 weeks): morning sickness, fatigue, very early development. 12-week scan confirms viability and dating. Second trimester (14-27 weeks): often called the 'easy' trimester - energy returns, baby movements felt around 18-20 weeks. 20-week scan checks anatomy. Third trimester (28-40 weeks): rapid growth, more discomfort, preparation. Birth typically between 37-42 weeks.

Key NHS milestones: 12-week dating scan (free, confirms LMP-based date or adjusts it), 20-week anomaly scan (free, checks development), GTT around 26 weeks if at risk for gestational diabetes, midwife appointments throughout. Working out due date matters for: maternity leave eligibility, antenatal class scheduling, hospital booking, paternity leave timing for partner.

Cycle length: Naegele's rule assumes 28-day cycles. Longer cycles (32+ days) push the due date forward; shorter cycles pull it back. Conception date if known: more accurate than LMP for irregular cycles - add 266 days (38 weeks). Early ultrasound: most accurate when done at 6-13 weeks; later ultrasounds become less precise as variation among babies increases.

First-time pregnancy: tendency for slightly later delivery (average +5-8 days past due date). Subsequent pregnancies: slightly earlier average. Multiple pregnancy (twins): often delivered earlier (37 weeks instead of 40). High BMI, gestational diabetes, hypertension may all affect timing. Talk to midwife if cycle was abnormal or you're uncertain about LMP - they can adjust based on early scan and cycle history.

20+ weeks ahead: book antenatal classes (NCT, NHS, hypnobirthing, etc.), discuss leave with employer, write birth plan. 12 weeks ahead: hospital bag preparation, baby essentials shopping, meal prep planning. 6 weeks ahead: install car seat, prepare nursery, finalise birth plan. 2 weeks ahead: hospital bag at door, important contacts on phone, charger packed.

First-baby parents often over-buy preparation. Essential first-month items: car seat (legal requirement to leave hospital), 5-7 sleep suits, 5-7 vests, nappies (newborn size for first 2-3 weeks then size 1), changing mat, lots of muslin cloths, basic toiletries, breast/bottle supplies. Most baby gear bought in first month gets used; most bought past first 6 months goes unused. Use the [Days Until Calculator](/days-until-calculator) for general countdown; this tool is pregnancy-specific.