Due Date Calculator: Pregnancy Weeks and Milestones
Our due date calculator estimates when your baby is likely to arrive. Work it out from the first day of your last period, a known conception date or an IVF transfer. You also see how far along you are today, your trimester and the dates of common scans and tests.
How a Due Date Is Worked Out
A typical pregnancy lasts about 280 days, or 40 weeks, counted from the first day of the last menstrual period. Doctors count from that day because most people know it, while the exact day of conception is usually unknown. As a result, you are already considered two weeks pregnant on the day you conceive.
Conception usually happens about 14 days after the period starts in a 28 day cycle. From conception, a pregnancy lasts about 266 days. Every method in this pregnancy calculator comes back to those two numbers.
Naegele's Rule
A German doctor described this shortcut in the early 1800s, and it is still taught today. Take the first day of your last period, add one year, subtract three months and add seven days. A last period on January 5, 2026 gives a due date of October 12, 2026, which matches the due date calculator.
How to Use the Due Date Calculator
- Choose your method: last period, conception date, IVF transfer or a due date you already have.
- Pick the date. For the last period, enter the first day of full bleeding.
- Enter your average cycle length if you use the last period method. A longer cycle moves the due date later.
- For IVF, choose whether the embryo was 3, 5 or 6 days old at transfer.
The results show your estimated due date, how far along you are today and your current trimester. You also get the days left and the likely conception date. A table lists the dates of common scans and the start of each trimester.
Due Date Calculator Examples
From Your Last Period
Your last period started on Monday, January 5, 2026. Your cycle is 28 days long. The pregnancy calculator adds 280 days and shows a due date of Monday, October 12, 2026. With a 32 day cycle, ovulation comes four days later, so the due date moves to Friday, October 16.
From a Conception Date
If you know you conceived on January 19, 2026, the tool adds 266 days. The due date is again Monday, October 12, 2026. A known conception date skips the guesswork about when you ovulated.
From an IVF Transfer
For a five day embryo transferred on January 24, 2026, the IVF due date is the transfer date plus 261 days. That gives Monday, October 12, 2026 once more. A three day embryo transferred on January 22 also lands on October 12, because it is two days younger.
How Many Weeks Pregnant Am I?
Pregnancy weeks are written as completed weeks plus days, such as 9 weeks 3 days. Week 1 starts on the first day of your last period, so the first two weeks pass before conception. The due date calculator counts the days from that start to today and shows the result in this format.
To count your weeks by hand, count the days since your last period and divide by 7. The whole number is your weeks, and the remainder is your extra days. A pregnancy calculator saves you the counting and also handles cycles longer or shorter than 28 days.
| Trimester | Weeks | What usually happens |
| First | Week 1 to 13 weeks 6 days | Early scans, first prenatal visit, screening tests |
| Second | 14 weeks to 27 weeks 6 days | Anatomy scan, glucose test, first kicks |
| Third | 28 weeks to birth | Growth checks, birth planning, full term at 39 weeks |
Key Dates in Your Pregnancy
The table under the results turns your due date into a calendar of milestones. The pregnancy calculator builds it from the start of week 1, so every date moves when your due date moves. These are the dates for a last period on January 5, 2026.
| Week | Date | Milestone |
| 8 | March 2, 2026 | First prenatal visit window |
| 12 | March 30, 2026 | First trimester screening window |
| 20 | May 25, 2026 | Anatomy scan window |
| 28 | July 20, 2026 | Third trimester begins |
| 37 | September 21, 2026 | Early term |
| 39 | October 5, 2026 | Full term |
| 40 | October 12, 2026 | Due date |
Your doctor or midwife may book things on slightly different weeks. Treat the list as a planning guide and follow the schedule your care team gives you. A due date calculator cannot replace that advice.
How Accurate Is a Due Date?
Only about 4% of babies arrive on the exact due date. Most are born within two weeks of it. Think of the due date as the middle of a window rather than a deadline.
An early ultrasound is the most precise way to date a pregnancy. In the first trimester, doctors measure the baby and compare its size with your period date. If the two differ by more than about five to seven days, they usually switch to the scan date.
Irregular cycles make the last period method less reliable. If you are not sure of your dates, use the due date calculator as a first guess and confirm it at your first scan. Enter the new date in the due date mode of the pregnancy calculator.
IVF and Known Conception Dates
IVF gives the most precise dates because the age of the embryo is known to the day. A five day blastocyst is treated as if conception happened five days before the transfer. Clinics use the same math, so your IVF due date here should match theirs.
A known conception date from ovulation tests is almost as useful. Remember that sperm can live for days, so the date of sex is not always the date of conception. If you are unsure, use the last period method in the pregnancy calculator instead.
Planning Around Your Due Date
A pregnancy calculator is handy for more than counting weeks. Many parents use the result of a due date calculator to plan leave from work and arrange help at home. Knowing the trimester dates also helps you plan travel while you still feel well.
Many airlines ask for a doctor's letter late in pregnancy, and some will not fly you in the final weeks. Check before you book a late trip. Pack a hospital bag by about 36 weeks, since a baby can arrive any time from 37 weeks.
Share your dates with your partner or family so everyone plans around the same window. Run the pregnancy calculator again if your doctor gives you a new date after a scan. A quick update keeps every milestone in the table correct.
Why Use Our Pregnancy Calculator
It covers four methods, adjusts for cycle length and shows a full milestone table. Every result comes with the formula behind it, so you can check each step. It is a planning aid, not medical advice, so share your dates with your doctor or midwife. Pick a date and find your due date now.
Frequently asked questions
Is this due date calculator free?
Yes, it is free with no sign up and works right in your browser.
How is a due date calculated?
Add 280 days to the first day of your last period, or 266 days to the conception date.
How many weeks pregnant am I at conception?
You are about 2 weeks pregnant, because weeks are counted from your last period.
Can my due date change?
Yes, your doctor may change it after an early ultrasound.
Does the pregnancy calculator work for long cycles?
Yes, enter your cycle length and it moves the date by the extra days.
What is Naegele's rule?
Add one year, subtract three months and add seven days to the first day of your last period.
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