EDD (Estimated Due Date) Calculator

EDD stands for estimated due date: the date your baby is expected to arrive. By convention it is 40 weeks (280 days) after the first day of your last menstrual period. It is an estimate rather than an appointment. In a study of nearly 19,000 births, only 5% happened on the estimated date, and about two in three came within a week of it. Your doctor uses it to time your antenatal checks and scans.^{[1, 4]}

Yes. Enter the first day of your last period, your conception date or your IVF transfer details. The calculator will estimate your due date and show how many weeks and days pregnant you are, along with your current trimester. If you already have a confirmed EDD, select “I know my date” and enter it instead.

From your last period, add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, add or subtract the difference; a 31 day cycle adds 3 days. From a conception or ovulation date, add 266 days. For example, a last period starting on 1 July 2026, or conception on 15 July 2026, both give an EDD of 7 April 2027. If your doctor has already given you a due date from a scan, use that date instead.^[1]

For IVF, the EDD is counted from your embryo transfer date, not your last period: add 261 days for a day 5 blastocyst transfer, 263 days for a day 3 embryo transfer, or 266 days from the day of egg retrieval. These are one formula, 266 days minus the embryo’s age at transfer. A frozen transfer uses the same count as a fresh one, because the embryo stays the same age while frozen. For example, a day 5 transfer on 20 July 2026 gives an EDD of 7 April 2027. In this calculator, choose IVF transfer and pick the stage your clinic transferred.^[1]

A calculator is only as accurate as the date you give it. About half of women accurately recall the first day of their last period, and cycle lengths and ovulation vary, so a first trimester dating ultrasound, up to 13 weeks 6 days, is the most accurate way to confirm your dates.^[1]

If your cycles are irregular or you are unsure of your last period date, a period-based estimate is less reliable, and adjusting the cycle length cannot account for variable ovulation. An early dating scan, around weeks 7 to 9, measures your baby directly and gives a much more accurate estimate. You should also mention irregular cycles at your first O&G appointment.^{[1, 16]}

Yes. If your first trimester scan measurement differs from your period-based estimate by more than about 5 to 7 days, your doctor will usually re-date the pregnancy based on the scan. After that, the due date normally stays fixed. Guidance considers a pregnancy without a scan confirming the due date before 22 weeks to be less reliably dated.^[1]

Many women have their first appointment and dating scan between weeks 6 and 12, when a heartbeat can usually be seen on ultrasound. Book earlier if you have bleeding, severe pain, a history of miscarriage or ectopic pregnancy, or a medical condition such as diabetes or thyroid disease.^[7]

OSCAR (One-Stop Clinic for Assessment of Risk) is the name commonly used in Singapore for combined first trimester screening for chromosomal conditions. It pairs a nuchal translucency ultrasound with a blood test and is done between 11 weeks and 13 weeks 6 days. It is one of the few appointments with a hard deadline, so it helps to book early.^[9]

Your timeline shows suggested dates for pregnancy scans, screening tests and vaccinations based on your estimated due date. These include your dating scan, first-trimester screening, detailed anomaly scan and gestational diabetes screening. Confirm which appointments you need and their exact timing with your O&G specialist.