Pregnancy Due Date Calculator

A pregnancy due date is typically calculated as 280 days (40 weeks) from the first day of your last menstrual period (LMP). This standard is used because ovulation and conception occur approximately two weeks after the start of the LMP, and pregnancy is conventionally counted from the LMP. So while actual conception is around week 2, pregnancy 'starts' at week 0. Due dates are an estimate — only about 4% of babies are born on their exact due date. A normal full-term birth occurs anywhere between 38 and 42 weeks gestation. Early ultrasound scans (especially an 8–12 week dating scan) may be used to confirm or adjust the estimated due date based on foetal measurements. In New Zealand, your Lead Maternity Carer (LMC) will confirm your due date at your first antenatal appointment. Source: NZ Ministry of Health — Pregnancy (health.govt.nz).

Naegele's rule is the standard medical formula for estimating a pregnancy due date. Developed by German obstetrician Franz Karl Naegele in the early 19th century, the rule calculates the estimated date of delivery (EDD) by taking the first day of the last menstrual period (LMP), adding one year, subtracting three months, and adding seven days. For example, if your LMP was 1 May 2025, the EDD would be: 1 May 2025 + 1 year - 3 months + 7 days = 8 February 2026. This is equivalent to adding 280 days (40 weeks) to the LMP. Naegele's rule assumes a 28-day menstrual cycle with ovulation on day 14, so adjustments may be needed for women with irregular or longer cycles. Despite its age, Naegele's rule remains the standard first-line due date calculation used worldwide and in New Zealand maternity care. Source: NZ Midwifery Council (midwiferycouncil.health.nz).

In New Zealand, you should register with a Lead Maternity Carer (LMC) — usually a midwife — as early as possible in your pregnancy, ideally before 10 weeks gestation. Early registration ensures you receive all recommended first-trimester care, including the combined screening test (offered between 10–14 weeks) and your first dating ultrasound. Finding an LMC early is particularly important as some areas of New Zealand have midwife shortages and LMCs may have limited availability. You can search for available LMCs through the Find Your Midwife website (findyourmidwife.co.nz). Your LMC will coordinate all your antenatal care throughout pregnancy, attend your birth, and provide postnatal care for up to six weeks after birth. All LMC maternity care is fully funded by the government for eligible New Zealanders. Source: NZ Ministry of Health — Maternity Services (health.govt.nz).

New Zealand provides free maternity care through the publicly funded Lead Maternity Carer (LMC) system. This covers: all antenatal appointments with your LMC throughout pregnancy; recommended screening tests including the first-trimester combined screen and anatomy ultrasound at 18–20 weeks; labour and birth support from your LMC; and postnatal care for up to six weeks after birth including home visits. Hospital-based care, if required, is funded through DHB (now Te Whatu Ora — Health New Zealand) services. ACC covers treatment costs for any injuries occurring during birth. There is no charge for publicly funded maternity services for New Zealand citizens and permanent residents. Additional elective services — such as private obstetrician care, additional ultrasounds not clinically indicated, or private birth suites — involve out-of-pocket costs. Source: NZ Ministry of Health — Maternity Services (health.govt.nz).