This is an estimate based on standard obstetric dating rules (Naegele's rule for LMP - 280 days / 40 weeks - and 266 days from conception or IVF retrieval). Only about 5% of babies arrive on their exact due date. Your doctor's ultrasound-based estimate is more accurate; use this for planning purposes only, not medical advice.
Estimate Your Pregnancy Due Date
The Tools Kit's free Due Date Calculator estimates when your baby is due from the first day of your last menstrual period, a known conception date, or an IVF embryo transfer date. With the last-period method it also works out how many weeks pregnant you are today and which trimester you are in, so it doubles as a simple pregnancy week calculator.
Due date = first day of last period + 280 days (40 weeks). An LMP of March 10, 2026 gives an estimated due date of Tuesday, December 15, 2026. Everything is calculated in your browser, and the dates you enter are never sent anywhere.
How to Use the Due Date Calculator
- 1
Choose how to calculate
In the "Calculate from" menu, pick Last menstrual period (LMP), Conception date, or IVF transfer date.
- 2
Enter the date
Enter the first day of your last period, your conception date, or your embryo transfer date. For IVF, also choose whether it was a Day 3 or Day 5 (blastocyst) transfer.
- 3
Read your estimated due date
The estimated due date appears instantly, written out in full with the day of the week.
- 4
Check how far along you are
With the LMP method, the calculator also shows your current gestational age in weeks and days and which trimester you are in, measured up to today.
Switching methods keeps each date you entered, so you can compare an LMP-based estimate with a conception-based one in a few clicks.
Three Ways to Calculate a Due Date
All three methods aim at the same point: 40 weeks of gestational age, counted from the first day of the last period. They simply start from different known dates.
- Last menstrual period (Naegele's rule): LMP + 280 days. This is the standard method doctors and midwives start with, because most people know when their last period began.
- Conception date: conception + 266 days (38 weeks). Conception is assumed to happen about two weeks after the LMP, so this lands on the same date as the LMP method for a typical 28-day cycle.
- IVF transfer date: transfer + (266 − embryo age). A day-5 blastocyst transfer adds 261 days and a day-3 transfer adds 263 days, because the embryo was already that many days old when it was transferred.
Worked example: an LMP of March 10, 2026, a conception date of March 24, 2026, a day-5 transfer on March 29, 2026 and a day-3 transfer on March 27, 2026 all give the same estimated due date of December 15, 2026. To count the days between any other two dates, such as from today to your due date, use the days calculator.
How Many Weeks Pregnant Am I?
Pregnancy is measured in gestational age: completed weeks and days since the first day of your last period, not since conception. That is why you are already considered about two weeks pregnant at conception, and why a full-term pregnancy is described as 40 weeks.
When you use the LMP method, the calculator counts the days from your LMP to today's date and shows the result in weeks and days. With an LMP of March 10, 2026, on October 1, 2026 you would be 205 days along, shown as 29w 2d, which falls in the third trimester. The calculator uses weeks 0-13 for the first trimester, 14-27 for the second and 28 onward for the third. If you entered a conception or IVF date instead, switch to the LMP method to see your current week.
How Accurate Is a Due Date?
A due date is an estimate of the middle of a likely delivery window, not a deadline. Only about 5% of babies arrive on the exact date, and most are born within about two weeks either side of it. Naegele's rule also assumes a 28-day cycle with ovulation around day 14; this calculator has no cycle-length setting, so if your cycles run long or short your true due date may be several days later or earlier.
IVF dates are usually the most precise because the embryo's age is known exactly. For natural pregnancies, an early ultrasound dating scan measures the baby directly and is generally more reliable than a last-period estimate, so use this calculator for planning and follow the date your doctor or midwife gives you. This tool is not medical advice.
Common uses
- Getting a first estimate of your due date before your first prenatal appointment
- Checking how many weeks pregnant you are and which trimester you are in today
- Working out an IVF due date from a day-3 or day-5 embryo transfer
- Cross-checking a due date given by a provider or pregnancy app
- Planning parental leave, a nursery, and the budget for the months ahead
Once you have a date, the baby cost calculator helps you estimate first-year expenses, and the paycheck calculator is useful for seeing how take-home pay changes while you plan time off. For health tracking before and during pregnancy, the BMI calculator shows the pre-pregnancy BMI that weight-gain guidance is usually based on, and the calorie calculator estimates your baseline daily energy needs to discuss with your provider. After the birth, the age calculator tracks your baby's exact age in years, months and days. You can find more planning tools among our free calculators.
Pregnancy dating terms explained
| Term | What it means here |
|---|---|
| Estimated due date (EDD) | The date 40 weeks after the first day of the last menstrual period; also called the estimated date of delivery or confinement |
| LMP | Last menstrual period: the first day of the most recent period, the standard starting point for pregnancy dating |
| Naegele's rule | The classic dating rule: LMP plus 280 days, or equivalently LMP plus one year, minus three months, plus seven days |
| Gestational age | How far along a pregnancy is, counted in weeks and days from the LMP rather than from conception |
| Fetal age | Age counted from conception; about two weeks less than gestational age |
| Day 3 / Day 5 transfer | The age of the embryo, in days after egg retrieval, when it is transferred in IVF; a day-5 embryo is called a blastocyst |
| Trimester | One of three stages of pregnancy; this calculator uses weeks 0-13, 14-27 and 28 onward |
Frequently Asked Questions
From the last menstrual period, the due date is the first day of the LMP plus 280 days (40 weeks), which is Naegele’s rule. From a known conception date it is conception plus 266 days (38 weeks). For IVF it is the transfer date plus 266 days minus the embryo’s age, so 261 days for a day-5 transfer and 263 days for a day-3 transfer.
Add 280 days to the first day of your last menstrual period. An LMP of March 10, 2026 gives a due date of December 15, 2026. A quick manual shortcut is to add one year, subtract three months and add seven days; the calculator does the exact day count for you.
Yes. Choose "Conception date" and enter the date you conceived; the calculator adds 266 days (38 weeks). A conception date of March 24, 2026 gives a due date of December 15, 2026, the same result as an LMP two weeks earlier.
Choose "IVF transfer date", enter the embryo transfer date and pick Day 3 or Day 5. The calculator adds 266 days minus the embryo’s age: 261 days for a day-5 blastocyst transfer and 263 days for a day-3 transfer. A day-5 transfer on March 29, 2026 gives a due date of December 15, 2026.
Choose the LMP method and enter the first day of your last period. The calculator counts the days from that date to today and shows your gestational age in weeks and days, such as 29w 2d, along with your trimester. This is shown only for the LMP method.
This calculator treats weeks 0 through 13 as the first trimester, weeks 14 through 27 as the second, and week 28 onward as the third, counted from the first day of your last period. The trimester appears next to the due date when you use the LMP method.
It gives a statistical estimate, not a prediction of the exact day. Only about 5% of babies are born on their due date, and most arrive within about two weeks either side. The LMP method assumes a 28-day cycle with ovulation around day 14, so an early ultrasound dating scan is usually more accurate.
Naegele’s rule assumes a 28-day cycle, and this calculator has no cycle-length setting. If you ovulate later or earlier than day 14, your true due date shifts by roughly the same number of days. If you know when you conceived, the conception-date method avoids the cycle assumption; otherwise rely on your provider’s ultrasound date.
By convention, pregnancy is dated from the first day of the last period, about two weeks before conception in a typical cycle, because that date is usually known while the exact day of conception is not. So 40 weeks of gestational age is about 38 weeks after conception, which is why the conception method adds 266 days instead of 280.
No. The due date is calculated entirely in your browser from the dates you enter, and nothing is sent to a server or saved. There is no signup and no limit on how many dates you try.
Reviewed by Raja Jahangir · Last reviewed: October 2026
How is a pregnancy due date calculated?
A due date from your last period uses Naegele's rule: the first day of the last menstrual period plus 280 days, or 40 weeks. From a known conception date it is conception plus 266 days. For IVF, it is the transfer date plus 266 days minus the embryo's age, so a day-5 transfer adds 261 days.
How accurate is a due date?
A due date is an estimate, not a deadline: only about 5% of babies arrive on the exact day, and most are born within two weeks either side. The last-period method assumes a 28-day cycle with ovulation on day 14, so an early ultrasound dating scan is more accurate and doctors usually rely on it.
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