Pregnancy Due Date Calculator — Find Your Due Date
Calculate your estimated due date by last menstrual period, conception date, or IVF transfer. See your gestational age, trimester, and key milestones. No signup, runs in your browser.
Estimated due date only. Fewer than 5% of babies are born on their due date — actual delivery typically falls within 2 weeks either side. This tool does not constitute medical advice. Always consult your healthcare provider.
How the Pregnancy Due Date Calculator Works
- 1Choose your calculation method: Last Period (LMP) for the standard approach, Conception Date if you know when you ovulated, or IVF Transfer for IVF pregnancies.
- 2Enter your date. For LMP, also confirm your cycle length — the calculator adjusts for cycles longer or shorter than 28 days automatically.
- 3Read your estimated due date, current gestational age in weeks and days, and trimester from the results card.
- 4Review the milestone timeline — showing key dates like the 12-week scan, anatomy scan, viability threshold, and term definitions with their actual calendar dates.
Why Due Date Estimates Are Approximate
The estimated due date (EDD) is calculated assuming ovulation occurred on day 14 of a 28-day cycle — but ovulation varies even in regular cycles, and implantation timing adds further variability. Studies show that spontaneous labour at term follows a distribution centred around the due date, with a standard deviation of about 8–9 days. Only 4–5% of births occur on the exact EDD. Your healthcare provider may revise the due date after an early ultrasound, which is the most accurate dating method available before 13 weeks.
Pregnancy Milestones to Know
6 weeks — heartbeat
A fetal heartbeat is typically visible on a transvaginal ultrasound from around 6 weeks gestational age. The embryo is about 3–5 mm at this stage. An abdominal ultrasound may not detect it this early.
12 weeks — end of 1st trimester
The 12-week scan includes nuchal translucency (NT) measurement for chromosomal risk screening and confirms viability. Miscarriage risk drops significantly after this point. Most people share their pregnancy news around this milestone.
20 weeks — anatomy scan
The mid-pregnancy anatomy scan (also called the anomaly scan) examines fetal development in detail — brain, heart, spine, limbs, and organs. It can also reveal sex if desired. This is typically the most comprehensive ultrasound of the pregnancy.
24 weeks — viability
At 24 weeks, survival rates with intensive NICU care reach roughly 50–70%. This is the legal and clinical threshold for viability in most countries. Each additional week significantly improves outcomes: by 28 weeks, survival rates exceed 90%.
37 weeks — early term
Babies born from 37 weeks are no longer classified as preterm. However, outcomes continue to improve with each additional week through 39–40. Elective delivery before 39 weeks without medical indication is generally not recommended.
39–40 weeks — full term
Full term (39 weeks 0 days to 40 weeks 6 days) is when outcomes are typically best. Lung maturity, brain development, and feeding ability are most reliable at this stage. Most uncomplicated pregnancies are managed expectantly until at least 39 weeks.
Frequently Asked Questions
How is the due date calculated?
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle — the calculator adjusts automatically if your cycle is shorter or longer. For conception date, 266 days (38 weeks) are added. For IVF, the calculation accounts for the age of the embryo at transfer: 261 days for a 5-day blastocyst and 263 days for a 3-day embryo.
What is gestational age?
Gestational age is how far along a pregnancy is, measured in weeks and days from the first day of the last menstrual period — not from conception. This means gestational age includes approximately two weeks before conception actually occurred. A "4-week pregnant" reading means the LMP was 4 weeks ago; the embryo itself is about 2 weeks old. This is the universal standard used by obstetricians and ultrasound measurements.
Will my baby actually arrive on the due date?
Fewer than 5% of babies are born on their estimated due date. Most arrive within a window of two weeks before to two weeks after. A pregnancy is considered "term" between 37 and 42 weeks. Full term — when outcomes are typically best — is 39–40 weeks. A baby born before 37 weeks is preterm; after 42 weeks is post-term.
My cycle is not 28 days — does that change my due date?
Yes. Naegele's Rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer, ovulation occurs later and the due date shifts forward. If shorter, it shifts back. The calculator adjusts automatically: for every day your cycle differs from 28, the due date moves by one day. A 32-day cycle gives a due date 4 days later than the standard 28-day calculation; a 24-day cycle gives a due date 4 days earlier.
How does IVF due date calculation work?
In IVF, the embryo's age at transfer is known precisely. A 5-day blastocyst is 5 days old at transfer, so conception-equivalent occurred 5 days before transfer. The due date is calculated as transfer date + (266 − 5) = 261 days. For a 3-day embryo, it is transfer date + (266 − 3) = 263 days. This is more precise than LMP-based calculation because implantation timing is exact.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. Nothing you enter is sent to a server or stored anywhere. Your health information stays completely private.
What is the difference between early term, full term, and post-term?
Term definitions (per ACOG): Early term is 37 weeks 0 days to 38 weeks 6 days. Full term is 39 weeks 0 days to 40 weeks 6 days — when outcomes are typically best. Late term is 41 weeks 0 days to 41 weeks 6 days. Post-term is 42 weeks and beyond, when monitoring intensifies and induction is often discussed. Preterm is before 37 weeks.
When will my due date change after an ultrasound?
An early ultrasound (before 13 weeks) is the most accurate method for determining gestational age and may revise the LMP-based estimate. If the ultrasound dating differs by more than 5–7 days from the LMP calculation, most providers will update the due date to match the ultrasound. Later ultrasounds are less accurate for dating because fetal growth becomes more variable.