Due Date Calculator

ASEAN DUE DATE HEALTH PREGNANCY WEEKS

About this tool

Calculate your pregnancy due date and current week — enter your last period or conception date.

Calculate your pregnancy due date and current week — enter your last period or conception date. See trimester, milestones and key scan dates. Free, no signup.

RT-HLT-010 · Health & Fitness

First day of your last period Enter the first day of your most recent menstrual period.

Average cycle length Default is 28 days. Adjust if your cycle is shorter or longer.

Your estimated due date

Current Week

Trimester

Countdown

Pregnancy Progress

Key Milestone Dates

This is an estimate only. Your actual due date can only be confirmed by your doctor via ultrasound. Due dates calculated from LMP assume a regular cycle and ovulation on day 14. Always consult your healthcare provider for personalised advice.

How to Use the Due Date Calculator

Choose LMP or Conception Date mode

If you know the first day of your last menstrual period, use the LMP tab — this is the most common input method used by doctors. If you know your approximate conception date (e.g. from an IVF transfer), use the Conception Date tab.

Enter the date

Select the date using the date picker. In LMP mode, also adjust the cycle length if your cycle is not the default 28 days — the calculator adds or subtracts days accordingly. Results appear the moment you pick a date.

See your due date and current week

Your estimated due date is displayed prominently. Below it, the current pregnancy week, trimester, and days remaining are shown. The progress bar visualises your position in the 40-week journey, with trimester boundaries clearly marked.

Review key milestone dates

The milestone list shows the dates for your Week 8 first visit, Week 12 NT scan, Week 20 anatomy scan, and other key appointments. Each milestone shows the calendar date and how many weeks away (or ago) it falls.

Pregnancy Timeline — Understanding Your 40 Weeks

How Due Dates Are Calculated: Naegele's Rule

The most widely used method for calculating a pregnancy due date is Naegele's Rule, first described by German obstetrician Franz Karl Naegele in 1812. The rule is simple: take the first day of the last menstrual period (LMP), add one calendar year, subtract three months, and add seven days — which is arithmetically equivalent to adding 280 days (40 weeks) to the LMP date.

The formula assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. If your cycle is shorter or longer, this calculator adjusts accordingly — for each day your cycle differs from 28 days, the due date shifts by the same number of days. A woman with a 35-day cycle, for example, ovulates later, so her due date is pushed forward by seven days relative to the standard calculation.

Despite being over two centuries old, Naegele's Rule remains the global standard for initial due date estimation. Studies consistently show that approximately 95% of babies are born within two weeks of their calculated due date. However, ultrasound dating — particularly the first-trimester crown-rump length (CRL) measurement taken between weeks 8 and 14 — is more accurate, as it directly measures fetal size rather than relying on menstrual history. IVF pregnancies use a different formula: due date is calculated from the embryo transfer date plus 266 days (38 weeks), or adjusted for the embryo's developmental stage at transfer.

Prenatal Care in Singapore

Singapore offers one of the most comprehensive antenatal care systems in Southeast Asia. KK Women's and Children's Hospital (KKH), located in Bukit Timah Road, is Singapore's largest specialist women's and children's hospital and delivers over 10,000 babies annually, making it one of Asia's busiest maternity facilities. The National University Hospital (NUH) in Kent Ridge and Thomson Medical Centre in Novena are also major maternity providers. Mount Alvernia Hospital in Thomson Road and Gleneagles Hospital are popular private options.

"Singapore's KK Women's and Children's Hospital delivers over 10,000 babies per year — it's one of Asia's largest maternity hospitals and is fully equipped for high-risk pregnancies."

For subsidised care, all Singapore residents can access antenatal services at polyclinics managed by SingHealth Polyclinics and National Healthcare Group Polyclinics. The polyclinic antenatal programme covers routine checkups, blood tests, and referrals to restructured hospitals at heavily subsidised rates. The government's Baby Bonus scheme provides cash gifts of up to S$11,000 for the first and second child (as of 2024 enhancements), plus Child Development Account (CDA) co-savings of up to S$9,000 for the third and beyond. Singapore Medisave covers approved maternity-related expenses, including delivery and selected outpatient antenatal visits, under MediShield Life.

It is strongly advisable to book your first prenatal appointment as soon as pregnancy is confirmed — ideally before week 12 — to schedule the nuchal translucency (NT) scan, which screens for chromosomal conditions such as Down syndrome. The NT scan must be performed between weeks 11 and 14 for accurate results.

The Three Trimesters — What Happens When

Pregnancy is conventionally divided into three trimesters. The first trimester (weeks 1–13) is the most critical developmental period: implantation occurs around week 3–4, the embryo's major organs begin forming (organogenesis) between weeks 5–10, and the risk of miscarriage is highest during this phase (approximately 10–15% of known pregnancies). Morning sickness — nausea and vomiting — affects up to 80% of pregnant women during the first trimester, typically peaking around weeks 8–10.

The second trimester (weeks 14–27) is generally considered the most comfortable. The miscarriage risk drops sharply after week 12. Baby movements are first felt (quickening) typically between weeks 16–22. The 20-week anatomy scan — the detailed structural ultrasound — checks for physical abnormalities and reveals the baby's sex if parents wish to know. Many women experience improved energy and reduced nausea during this period.

The third trimester (weeks 28–40) is marked by rapid fetal growth. Braxton Hicks contractions — practice contractions — become noticeable. The Group B Streptococcus (GBS) test is performed at around week 35–36; GBS bacteria is present in approximately 25% of pregnant women and can pose risks to the newborn if not managed. In Singapore, the NICU at KKH is equipped to handle extremely premature births, including infants born as early as 23 weeks gestation. At 37 weeks, a pregnancy is considered "term" by the World Health Organization — a baby born at 37 weeks is no longer classified as premature.

10 Facts About Pregnancy and Due Dates

Naegele's Rule was first published in 1812 by German obstetrician Franz Karl Naegele and is still used worldwide today.

About 95% of babies are born within two weeks of their calculated due date — only about 5% are born exactly on the due date itself.

KKH delivers over 10,000 babies per year, making it one of the highest-volume maternity hospitals in Asia.

Singapore's Baby Bonus scheme offers cash gifts and CDA co-savings worth up to S$11,000 and beyond for qualifying births.

Singapore's total fertility rate (TFR) was 1.04 in 2023 — among the lowest in the world, well below the replacement rate of 2.1.

Ultrasound dating using crown-rump length in weeks 8–14 is more accurate than LMP-based calculation, especially for irregular cycles.

The average pregnancy lasts 280 days (40 weeks) from LMP — but "term" is defined as any birth between 37 and 42 weeks.

For IVF embryo transfers, due date is calculated from the transfer date plus 266 days, adjusted for the embryo's age at transfer.

The Group B Strep (GBS) test at week 35–36 screens for bacteria that can infect newborns during delivery — treatment is simple and effective.

Singapore Medisave can be used for approved maternity-related expenses including delivery and selected antenatal outpatient visits under MediShield Life.

Frequently Asked Questions

Using Naegele's Rule: your due date = first day of last period + 280 days (40 weeks). If your cycle length is not 28 days, the calculator adjusts: each day above or below 28 shifts the due date by one day. For conception date mode, due date = conception date + 266 days (38 weeks).
Naegele's Rule is the standard method for estimating a pregnancy due date, published in 1812. It adds 280 days (40 weeks) to the first day of the last menstrual period, assuming a 28-day cycle with ovulation on day 14. It has been used by doctors worldwide for over 200 years.
About 95% of babies are born within two weeks of the calculated due date. Only around 5% are born exactly on the due date. Ultrasound dating (especially the first-trimester NT scan) is more accurate than LMP-based calculation and may adjust your due date. Your doctor's ultrasound date is always the authoritative figure.
Use the cycle length selector to choose your average cycle length (21–35 days). The calculator adjusts the due date accordingly. However, if your cycles are very irregular, the LMP method is less reliable — ultrasound dating at your first prenatal visit will give a more accurate result.
Yes. If your first-trimester ultrasound shows a crown-rump length that differs significantly from your LMP-based date, your doctor will revise your due date to match the ultrasound measurement. This is normal and does not indicate a problem — it simply means the ultrasound measurement is a more accurate indication of gestational age.
For a Day 5 blastocyst transfer, the due date is calculated as the transfer date + 261 days. For a Day 3 embryo transfer, it is transfer date + 263 days. You can use the Conception Date tab and enter your transfer date as an approximation — your IVF clinic will give you the precise adjusted date.
The WHO defines term birth as delivery between 37 weeks 0 days and 41 weeks 6 days. Preterm is before 37 weeks. Early term is 37–38 weeks; full term is 39–40 weeks; late term is 41 weeks; post-term is 42 weeks or more. Babies born before 28 weeks are considered extremely preterm and require intensive NICU care.
Going past your due date is very common — about 10% of pregnancies go beyond 41 weeks. Most Singapore hospitals will recommend induction of labour at 41 weeks, or 40–41 weeks for higher-risk pregnancies. Post-term (42+ weeks) carries increased risks, so your obstetrician will monitor you closely and discuss your options if you reach 41 weeks without going into labour.
Elective C-sections are typically scheduled at 39 weeks gestation or later to ensure full lung maturity. Your obstetrician will confirm the date once your due date is established via ultrasound. This calculator can help you estimate the 39-week window by looking at your due date minus one week.
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