Pregnancy Due Date Calculator
Find your estimated due date (EDD), how many weeks pregnant you are, your trimester and month, estimated conception date, and week-by-week milestones. Calculate from your last period, conception date, IVF transfer, an ultrasound, or a known due date — instantly and privately in your browser.
Last menstrual period
Enter the first day of your last menstrual period.
Default 28 days. Allowed range 20–45 days.
Calculated privately in your browser — nothing is uploaded or stored.
Choose a method above and enter your dates to see your due date and pregnancy progress.
For education only. An early ultrasound dating scan is the most accurate way to confirm your due date, especially with irregular cycles. Always follow your obstetrician’s advice.
How is a pregnancy due date calculated?
A due date is usually calculated by adding 280 days (40 weeks) to the first day of your last menstrual period — a method called Naegele’s rule. This calculator applies that formula, adjusts it for your cycle length, and also supports conception, IVF, ultrasound and known-due-date methods.
Pregnancy is measured in gestational age — weeks and days since the first day of your last period. Because a term pregnancy lasts about 40 weeks from that point, the estimated due date (EDD) marks 40 completed weeks. It is genuinely an estimate: roughly 4 in 100 babies arrive on the exact date, and most are born within two weeks either side.
Due date formulas
Each calculation method reduces to a simple day count. These are the formulas this tool uses:
| Method | Formula | Note |
|---|---|---|
| Last menstrual period (LMP) | LMP + 280 days + (cycle − 28) | Naegele's rule, adjusted for cycle length |
| Conception date | Conception + 266 days | Counts from fertilisation |
| IVF — Day-3 transfer | Transfer + 263 days | Embryo was 3 days old at transfer |
| IVF — Day-5 transfer | Transfer + 261 days | Blastocyst was 5 days old at transfer |
| Ultrasound dating | Scan date − GA at scan, then + 280 days | Most accurate in the first trimester |
| Known due date | Track backwards from the EDD | Derives week, trimester and conception |
Why is pregnancy counted from the last menstrual period?
Because the first day of your last period is a date most people can pinpoint, while the exact day of conception usually is not. Counting from the LMP is the long-standing clinical convention.
A side-effect is that you are counted as “pregnant” for about two weeks before conception actually happens. That is why gestational age is about two weeks more than the baby’s true (conceptional) age, and why 40 weeks — not 38 — describes a full-term pregnancy.
How accurate is a pregnancy due date calculator?
A calculator reliably applies the standard formulas, but the due date is only as good as the dates and assumptions you feed it. A first-trimester dating ultrasound is the most accurate method and is used to set the official due date when it disagrees with LMP dating.
LMP dating assumes a regular 28-day cycle with ovulation on day 14. If ovulation was earlier or later — common with irregular cycles — the estimate shifts. An early scan measures the baby directly (crown-rump length) and dates the pregnancy to within about 5–7 days. An online tool is excellent for planning, but it does not replace a clinical assessment.
What if my menstrual cycle is irregular?
With irregular cycles, ovulation timing is uncertain, so LMP-based dating is less reliable. Enter your average cycle length for a closer estimate, then rely on an early ultrasound to confirm the due date.
This calculator shifts the due date by (your cycle length − 28) days to account for later or earlier ovulation. If your cycles vary a lot, or you were on hormonal contraception recently, a dating scan is especially important.
How is an IVF pregnancy due date calculated?
For IVF, the embryo’s age is known, so the due date is counted from the transfer: a Day-3 transfer adds 263 days and a Day-5 (blastocyst) transfer adds 261 days.
IVF dating is usually more precise than natural-conception dating because there is no uncertainty about when fertilisation occurred. If you used a frozen embryo transfer, use the transfer date and the correct embryo day. Your fertility clinic’s dating takes precedence.
Can my due date change after an ultrasound?
Yes. A first-trimester dating scan measures the baby directly and is more accurate than period-based dating. If the scan and LMP dates differ by more than a few days, providers usually adopt the scan date.
To use scan dating here, choose the Ultrasound method and enter the scan date with the gestational age reported (for example, 12 weeks 3 days). The tool back-calculates your dates from that measurement. Later scans (after the first trimester) are less reliable for dating, so an early scan is preferred.
Pregnancy week and month guide
Pregnancy lasts about 40 weeks, commonly described as nine months. Here is how gestational weeks map to pregnancy months and trimesters:
| Month | Weeks | Trimester |
|---|---|---|
| Month 1 | 1–4 | First |
| Month 2 | 5–8 | First |
| Month 3 | 9–13 | First |
| Month 4 | 14–17 | Second |
| Month 5 | 18–22 | Second |
| Month 6 | 23–26 | Second |
| Month 7 | 27–30 | Third |
| Month 8 | 31–35 | Third |
| Month 9 | 36–40 | Third |
When does each trimester begin?
The first trimester is weeks 0–13 (up to 13w6d), the second is weeks 14–27, and the third begins at week 28 and continues until birth. A pregnancy is full term from 39 weeks; most babies are born between 37 and 42 weeks.
Each trimester has a distinct focus: organ formation and early screening in the first, growth and the anatomy scan in the second, and final growth and birth preparation in the third.
Pregnancy milestone timeline
These milestones are commonly associated with the weeks shown. Timing varies between healthy pregnancies — treat them as a guide, not a schedule. Your obstetrician decides which scans and tests you need and when.
- Week 2 — Estimated conception
Ovulation and fertilisation typically occur around week 2 of a 28-day cycle — roughly two weeks after the last menstrual period began.
- Week 3 — Implantation
The fertilised egg commonly implants in the uterine lining about 6–10 days after conception.
- Week 4 — Positive pregnancy test window
hCG usually rises enough for a home urine test to turn positive around the time of the missed period.
- Week 6 — First heartbeat detection
A fetal heartbeat can often be detected on a transvaginal ultrasound from about week 6, though timing varies.
- Week 8 — First antenatal (booking) visit
The first obstetric visit and dating scan are commonly done between weeks 6 and 10 in India to confirm dating and viability.
- Week 12 — First-trimester screening / NT scan
The nuchal translucency (NT) scan with combined screening is typically offered between 11w0d and 13w6d.
- Week 14 — Second trimester begins
Many people find early-pregnancy nausea and fatigue commonly ease as the second trimester starts.
- Week 16 — Quad / maternal serum screening
Second-trimester blood screening is typically offered around weeks 15–20 where first-trimester screening was not done.
- Week 20 — Anatomy (anomaly) scan
The detailed fetal anatomy scan (TIFFA) is typically recommended between 18 and 22 weeks.
- Week 24 — Fetal movement well established
Regular fetal movements ("quickening") are commonly felt by this stage; first-time mothers may notice them a little later.
- Week 26 — Glucose screening
Screening for gestational diabetes is typically recommended around weeks 24–28 (often earlier in India if risk factors are present).
- Week 28 — Third trimester begins
Antenatal visits usually become more frequent; an anti-D injection may be advised for Rh-negative mothers.
- Week 32 — Growth scan
A growth and well-being scan is commonly advised around weeks 30–34 to check fetal growth, liquor and the placenta.
- Week 37 — Full-term pregnancy reached
From 37 weeks a pregnancy is considered term. Most babies are born between 37 and 42 weeks.
- Week 40 — Estimated due date
The estimated due date marks 40 completed weeks. Only a small share of babies arrive exactly on this date — birth any time from 37 to 42 weeks is common.
How many weeks is a full-term pregnancy?
A pregnancy is considered full term from 39 weeks. 37–38 weeks is “early term”, 41 weeks is “late term”, and 42 weeks is “post term”. Most babies are born between 37 and 42 weeks.
Because of this range, the “delivery window” shown in your results (37–42 weeks) is a more realistic expectation than the single due-date day.
Can twins arrive before the estimated due date?
Yes — twins and other multiples commonly arrive earlier than single babies, often around 36–37 weeks, and are monitored more closely throughout pregnancy.
This calculator estimates a singleton due date. If you are expecting multiples, your obstetrician will set a dating and monitoring plan specific to your pregnancy.
What if I do not know my LMP?
If you don’t know your last period, use another method: conception date, IVF transfer date, a known due date, or the gestational age from an ultrasound. An early dating scan is the recommended way to establish dates.
Switch tabs at the top of the calculator to use whichever information you have.
Pregnancy due date calculator for India
Antenatal care in India follows national maternal-health guidance alongside advice from your obstetrician. The points below are general and commonly advised — your own plan should come from a qualified doctor.
Antenatal visits and scans commonly advised
A common pattern is monthly visits up to 28 weeks, fortnightly from 28–36 weeks and weekly thereafter. Scans commonly advised include a dating scan (6–10 weeks), an NT scan (11–13 weeks), a detailed anomaly scan / TIFFA (18–22 weeks) and a growth scan (30–34 weeks). Government initiatives such as PMSMA offer fixed-day antenatal check-ups.
Iron, folic acid, calcium and nutrition
Folic acid before and in early pregnancy, plus iron and folic acid (IFA) and calcium supplements through pregnancy, are commonly recommended in India to lower the risk of anaemia and support the baby’s development. Follow the dose your doctor advises.
Indian vegetarian and regional food ideas
- Vegetarian protein & iron: dal, rajma, chana, paneer, curd, soya, spinach and other leafy greens, and ragi.
- South Indian examples: idli/dosa with sambar, ragi malt, curd rice, drumstick and vegetable poriyal, buttermilk.
- North Indian examples: roti with dal and sabzi, rajma-chawal, paneer dishes, khichdi, seasonal fruit and dry fruits.
Foods to be careful with
Commonly advised to limit or avoid: raw or undercooked eggs and meat, unpasteurised milk and soft cheeses, high-mercury fish, unwashed produce, excess caffeine, and any alcohol. Wash fruits and vegetables well and prefer freshly cooked food.
Gestational diabetes
Gestational diabetes is common in India, and screening (often with an oral glucose test) is typically advised — sometimes in early pregnancy and again around 24–28 weeks. A balanced diet, portion control and activity, as guided by your doctor, help manage blood sugar.
Government maternal-health resources
See the Ministry of Health & Family Welfare, the National Health Mission maternal-health pages and PMSMA (linked in the references below). Above all, book care with a qualified obstetrician early in pregnancy.
Is an online pregnancy calculator medically accurate?
It uses medically accepted formulas and is a reliable planning aid, but it cannot examine you or replace a clinical assessment. Treat the result as guidance and confirm your dates with your obstetrician.
Frequently asked questions
How is a pregnancy due date calculated?
Most due dates use Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This calculator also adjusts for your cycle length and supports conception, IVF, ultrasound and known-due-date methods.
What is EDD in pregnancy?
EDD stands for estimated due date — the date, about 40 weeks from your last period, on which your baby is expected to arrive. It is an estimate: only about 4 in 100 babies are born exactly on the EDD.
How accurate is a pregnancy due date calculator?
An online calculator reliably applies the standard formulas, but the result is only as accurate as the dates you enter and the assumptions behind them. A first-trimester dating ultrasound is the most accurate way to set the due date.
Is an online pregnancy calculator medically accurate?
It uses medically accepted formulas and is useful for planning, but it cannot replace a clinical assessment. Your obstetrician may revise the date after an ultrasound. Use the result as guidance, not a diagnosis.
Why is pregnancy counted from the last menstrual period?
The first day of the last period is a date most people can identify, whereas the exact day of conception is rarely known. Counting from the LMP is the long-standing convention, so a term pregnancy is described as 40 weeks even though fertilisation happens around week 2.
Can my due date change after an ultrasound?
Yes. A first-trimester dating scan measures the baby directly and is more accurate than LMP dating. If the ultrasound date differs from the LMP date by more than a few days, your provider usually adopts the ultrasound date.
What if my menstrual cycle is irregular?
With irregular cycles, ovulation timing is uncertain, so LMP dating is less reliable. Enter your average cycle length for a better estimate, but rely on an early ultrasound to confirm the due date.
What if I do not know my LMP?
If you do not know your last period, use the conception date, an IVF transfer date, a known due date, or the gestational age from an ultrasound. An early dating scan is the recommended way to establish dates.
How is an IVF due date calculated?
For IVF, the due date is counted from the transfer. A Day-3 embryo transfer adds 263 days and a Day-5 (blastocyst) transfer adds 261 days, because the embryo age is already known precisely.
How many weeks is a full-term pregnancy?
A pregnancy is considered full term from 39 weeks. From 37 weeks it is "early term", 41 weeks is "late term" and 42 weeks is "post term". Most babies are born between 37 and 42 weeks.
When does each trimester begin?
The first trimester is weeks 0–13 (up to 13w6d), the second trimester is weeks 14–27, and the third trimester begins at week 28 and runs until birth.
How do I count my pregnancy in months?
Pregnancy is about 9 calendar months or 10 lunar months. Roughly: months 1–3 are the first trimester, months 4–6 the second, and months 7–9 the third. See the week-to-month table on this page.
How is gestational age different from fetal age?
Gestational age is counted from the first day of your last period. Fetal (conceptional) age is counted from fertilisation and is about two weeks less. Clinicians almost always use gestational age.
Can twins arrive before the estimated due date?
Yes. Twins and other multiples commonly arrive earlier than singletons — often around 36–37 weeks — and are monitored more closely. This calculator estimates a singleton due date; your obstetrician will guide multiple pregnancies.
What does it mean if I am overdue?
Going past your due date is common, especially in a first pregnancy. Providers monitor closely after 40–41 weeks and may discuss induction of labour if the pregnancy continues beyond about 41–42 weeks.
Can a baby be delivered earlier than the due date safely?
Babies born from 37 weeks are considered term and usually do well. Earlier (preterm) birth before 37 weeks may need extra care. Any decision about early delivery is individual and made with your obstetrician.
How does cycle length change the due date?
A cycle longer than 28 days means ovulation is later, so the due date moves later; a shorter cycle moves it earlier. This tool shifts the EDD by (cycle length − 28) days.
How accurate is a first-trimester dating scan?
A crown-rump-length measurement between roughly 8 and 14 weeks dates a pregnancy to within about 5–7 days, which is why it is preferred over LMP dating when the two disagree.
What is the difference between due date and delivery window?
The due date is a single estimated day at 40 weeks. The delivery window is the wider, more realistic range — usually 37 to 42 weeks — during which most healthy births occur.
Does the calculator store or share my information?
No. All calculations run locally in your browser. No dates, cycle length or results are uploaded, stored on a server, or shared, and no health data is placed in the page URL.
How often should I have antenatal check-ups in India?
Schedules vary, but a common pattern is monthly visits up to 28 weeks, fortnightly from 28 to 36 weeks, and weekly thereafter. Your obstetrician sets the schedule based on your pregnancy.
Which scans are commonly advised during pregnancy in India?
A dating scan (6–10 weeks), an NT scan (11–13 weeks), a detailed anomaly scan (18–22 weeks) and a growth scan (30–34 weeks) are commonly advised. Your doctor may recommend more based on your needs.
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This one calculator already covers pregnancy week, month, trimester, conception, IVF and EDD calculations — just switch methods at the top.
Medical disclaimer
This calculator and its content are for general information and education only. They are not a substitute for professional medical advice, diagnosis or treatment. Estimated due dates, weeks and milestones are approximations that vary between healthy pregnancies. Always consult a qualified obstetrician or gynaecologist about your pregnancy, and seek immediate care for any warning signs. Never disregard or delay medical advice because of something you read here.
Medical references
- ACOG — Methods for Estimating the Due Date (Committee Opinion 700)
- NHS — Pregnancy week-by-week
- WHO — Recommendations on antenatal care for a positive pregnancy experience
- Ministry of Health & Family Welfare, Government of India
- Pradhan Mantri Surakshit Matritva Abhiyan (PMSMA)
- National Health Mission — Maternal Health
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