What is a pregnancy due date calculator?
A pregnancy due date calculator estimates the date your baby is likely to be born, called the estimated due date (EDD) or estimated date of delivery. This free online due date calculator works from the first day of your last menstrual period (LMP), from a known conception date or from an IVF embryo transfer date. Along with the due date, it shows how many weeks pregnant you are today, your trimester, how many days are left and a week-by-week timeline of important scans and milestones.
How to calculate due date from LMP
Doctors in India and worldwide use Naegele's rule. A pregnancy lasts on average 280 days (40 weeks) counted from the first day of the last period, not from conception:
Due date = LMP + 280 days + (cycle length − 28 days)
- LMP = the first day of your last menstrual period
- 280 days = 40 weeks of pregnancy
- Cycle adjustment = the rule assumes a 28-day cycle with ovulation on day 14; for a 32-day cycle you ovulate about 4 days later, so the due date moves 4 days later
The quick hand method is: take the LMP, add 7 days, subtract 3 months and add 1 year.
Worked example
Your last period started on 1 January 2026 and your cycle is 28 days. 1 January + 280 days = 8 October 2026. By the hand method: 1 January + 7 days = 8 January, minus 3 months = 8 October, and plus 1 year gives 8 October 2026. If your cycles were 31 days long, the due date would be 3 days later, 11 October 2026.
Due date calculator from conception date
If you know the date you conceived – for example from ovulation tracking – the due date is conception date + 266 days (38 weeks). The calculator converts the conception date into an equivalent LMP two weeks earlier, so your gestational weeks match what your doctor uses.
Due date calculator for IVF
IVF dates are the most precise. For a day-5 blastocyst transfer, due date = transfer date + 261 days; for a day-3 embryo transfer, due date = transfer date + 263 days. Choose the right transfer type in the calculator.
How many weeks pregnant am I?
Pregnancy weeks are counted from the LMP, so at the moment of conception you are already "2 weeks pregnant". The calculator counts the days from your adjusted LMP to today and shows the result in weeks and days, such as 12 weeks 3 days. The weeks are grouped into three trimesters:
| Trimester | Weeks | Months (approx.) |
|---|---|---|
| First trimester | Week 1 – 13 | Months 1 – 3 |
| Second trimester | Week 14 – 27 | Months 4 – 6 |
| Third trimester | Week 28 – 40+ | Months 7 – 9 |
Due date calculator with milestones
The table in the result lists key dates for your pregnancy, month-wise and week-wise:
- Weeks 6–9: first ultrasound to confirm the heartbeat and date the pregnancy.
- Weeks 11–14: NT scan and double marker blood test – common in India as first-trimester screening.
- Weeks 18–22: anomaly scan (TIFFA or level II scan) to check the baby's development.
- Weeks 24–28: glucose tolerance test for gestational diabetes.
- Weeks 27–36: Tdap vaccination is recommended.
- Weeks 32–34: growth scan and Doppler, if your doctor advises.
- Weeks 37–42: the delivery window; full term is 39–40 weeks.
How accurate is a due date calculator?
Only about 4–5% of babies are born on their exact due date; most arrive within two weeks either side. The LMP method is accurate when your cycles are regular and you remember the date clearly. If your periods are irregular, you are unsure of the LMP or you conceived soon after stopping the pill, the ultrasound due date from a first-trimester scan (crown-rump length) is more reliable. Doctors usually change the EDD if the scan differs from the LMP date by more than about 5–7 days in the first trimester. Twins are usually delivered earlier, around 36–37 weeks.
Related tools
Planning a pregnancy? Use the ovulation calculator to find your fertile days, and the period calculator to predict your next periods. To count days between any two dates, use the date calculator.
LMP, conception, IVF or a scan: what to enter
Due date calculator based on LMP
The default mode uses the first day of your last period (LMP) and your cycle length, and gives the date doctors call the EDD. To calculate due date from lmp by hand, use Naegele's rule below.
Due date calculator with conception date
If you know the date of conception, switch the method and enter it. The calculator adds 266 days to that date.
After embryo transfer (IVF)
For IVF (in vitro fertilisation), the due date calculator counts from the embryo's age rather than from a period: choose the transfer type (day 3 or day 5 embryo) and enter the transfer date.
Due date calculator: how many weeks pregnant am I?
The results tell you how many weeks and days pregnant you are, and the due date calculator answers "how far along am I" in one line. The current week updates every day.
Due date calculator in months and weeks
Pregnancy is about 9 months and 1 week, or 40 weeks. The due date calculator shows which month of pregnancy you are in as well as the week, so you can plan month wise.
Due date calculator timeline, chart and ultrasound scans
The milestone table gives you a week-by-week timeline and chart, including the scans offered in India. Use the dates to book your ultrasound appointments, such as the NT and anomaly scans.
Due date calculator for twins
For twins the same 280-day rule applies, but read the result as the latest date – most twins arrive around 37 weeks.
Due date calculator if you know how many weeks
If a scan says you are, say, 10 weeks today, work backwards: today minus 10 weeks is your equivalent LMP. Enter that date and the due date calculator gives your result from today. Using the due date calculator in reverse works the same way: due date minus 280 days gives the LMP.
Due date calculator India and in Hindi
Indian doctors use the same Naegele's rule, so the result is reliable in India. In Hindi the due date is called "prasav ki anumanit tithi", and the answer is the same in any language.
Can it predict gender?
No due date calculator and gender predictor, and no Chinese gender chart, can predict a baby's sex; only ultrasound or genetic tests can. (In India, sex determination is illegal under the PCPNDT Act.)
hCG levels
Dating a pregnancy from hCG levels is not reliable, because hCG varies widely between pregnancies. Use your LMP or an early scan.
This online due date calculator is free of charge. It shows your expected delivery date and answers what the due date in pregnancy means: the day you reach 40 weeks.
Due date calculator formula (Naegele's rule)
The due date calculator formula is Naegele's rule: take the first day of your last period, add one year, subtract three months and add seven days. That is the same as adding 280 days (40 weeks). For a cycle longer or shorter than 28 days, add or subtract the difference. Example: last period on 10 January 2026 gives a due date of 17 October 2026.
Due date calculator and symptoms: what happens week by week
Early pregnancy symptoms such as a missed period, tender breasts, tiredness and nausea usually start around weeks 4–6, counted from the last period. Most people feel the baby move between weeks 18 and 22. Symptoms vary widely and do not confirm or change your due date; a pregnancy test and an early ultrasound do. Contact your doctor or midwife about bleeding, severe pain or any symptom that worries you.
Due date calculator app, NZ and South Africa
You do not need a due date calculator app; this page works in any phone browser. The method is the same worldwide, so midwives in NZ, obstetricians in South Africa and doctors in India all start from the last period and then confirm with a dating scan.
Due date calculator zodiac sign
Many parents like to know the zodiac sign of their due date. Keep in mind that only about 4% of babies arrive on the due date itself, and most are born within two weeks either side, so a due date near the edge of a sign (around the 20th–22nd of the month) could fall under either sign.
Due date calculator for sheep and other animals
Animals have different gestation lengths, so this human calculator does not apply to them. Sheep carry for about 147 days (roughly 142–152), goats about 150 days, cows about 283 days and dogs about 63 days. Add the gestation length to the mating date: a ewe mated on 1 October is due around 25 February.
Due date calculator for invoice and payment
In business, a due date calculator for an invoice adds the payment terms to the invoice date. For "Net 30", an invoice dated 15 March is due on 14 April; for "Net 45", on 29 April. For a credit card payment, the due date is usually about 15–20 days after the statement date; paying before it avoids interest and late fees. Count days between any two dates with the date calculator.
Frequently asked questions
How is the pregnancy due date calculated?
The standard method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last period, adjusted for cycle length. From a conception date, add 266 days.
How do I calculate my due date from my last period?
Take the first day of your last period, add 7 days, subtract 3 months and add a year. For example, an LMP of 1 January 2026 gives a due date of 8 October 2026. (Counting exactly 280 days, as this calculator does, can differ from the hand rule by a day or two in some months.)
How many weeks pregnant am I?
Count the days from the first day of your last period to today and divide by 7. The calculator does this and also shows your trimester.
Is the ultrasound due date more accurate than LMP?
An early ultrasound (before 14 weeks) is the most accurate way to date a pregnancy, especially if your cycles are irregular. Doctors may update your due date after it.
How is the due date calculated for IVF?
Add 261 days to a day-5 blastocyst transfer date, or 263 days to a day-3 embryo transfer date.
What is the due date for twins?
The due date is calculated the same way, but most twin pregnancies are delivered around 36–37 weeks, a few weeks earlier.
Can my due date change?
Yes. Your doctor may adjust it after the dating scan. Once set by an early scan, it usually does not change again.
What is the formula for calculating a due date?
Naegele’s rule: first day of your last period + 1 year − 3 months + 7 days, which equals 280 days after your last period.
How is an invoice due date calculated?
Invoice date plus the payment terms. For Net 30, an invoice dated 15 March is due on 14 April.
Last updated 2026-09-18