Due Date Calculator
Estimate your baby’s due date from your last period, a known conception date, or an IVF transfer date.
How to use this calculator
- Pick a tab: Last period, Conception, or IVF, based on what you know.
- Enter the date your method needs. Adjust cycle length if you’re using “Last period.”
- Tap Calculate my due date.
- See your estimated due date, current week of pregnancy, and full-term window.
Due Date Calculator: How Your Estimated Due Date Is Worked Out
What Is an Estimated Due Date (EDD)?
Your estimated due date, or EDD, is the day your baby is expected to be born if the pregnancy runs a full 40 weeks. Think of it as a reference point. Your doctor or midwife uses it to time checkups, order screening tests, follow your baby’s growth and help you prepare for birth.
Pregnancy is dated from the first day of your last menstrual period (LMP), not from conception. By the time you conceive, you are usually already two weeks into the count.
How Does a Due Date Calculator Work?
Most calculators use Naegele’s rule, which adds 280 days (40 weeks) to the first day of your last period. It assumes a 28-day cycle with ovulation around day 14.
To do it by hand, take the first day of your last period, add 7 days, subtract 3 months, and then adjust the year. Example: an LMP of 10 January becomes 17 January, then 17 October. That gives a due date of 17 October.
Cycles that are longer or shorter than 28 days move the date. If your cycle is 32 days, you probably ovulated about four days later than average, so your due date shifts about four days later. If you know your conception or ovulation date, the calculator can add 266 days (38 weeks) to it instead.
Due Date Methods at a Glance
| Method | What you need | Calculation | Best for |
|---|---|---|---|
| LMP (Naegele’s rule) | First day of last period | LMP + 280 days | Regular ~28-day cycles |
| LMP with cycle length | LMP and average cycle length | 280 days, adjusted for cycle length | Shorter or longer cycles |
| Conception/ovulation date | Known date | Date + 266 days | Women who track ovulation |
| IVF day-5 transfer | Transfer date | Transfer + 261 days | Blastocyst transfers |
| IVF day-3 transfer | Transfer date | Transfer + 263 days | Day-3 embryo transfers |
| Early ultrasound | Scan by your provider | Based on baby’s measurements | Uncertain dates, irregular cycles |
Calculating Your Due Date After IVF
IVF removes the guesswork because the clinic knows the embryo’s exact age. The calculation takes the transfer date, adds 266 days, then subtracts the days the embryo had already been developing. In practice:
- Day-5 transfer: add 261 days. A transfer on 15 June gives a due date of 3 March.
- Day-3 transfer: add 263 days. A transfer on 15 June gives a due date of 5 March.
(These examples assume a non-leap year.)
Can Your Due Date Change?
Yes, and it often does. Providers commonly revise the date after an early ultrasound, particularly if your periods are irregular, you aren’t sure when your last one started, or the baby’s measurements don’t match the expected size. A first-trimester ultrasound is usually the most dependable way to date a pregnancy, typically accurate to within about a week.
A new date doesn’t mean anything is wrong. It just means the date now fits your baby’s development better.
How Accurate Is Your Due Date?
Only around 5% of babies arrive on their due date. Most are born within two weeks either side, and the large majority between 38 and 42 weeks. Providers use these labels:
- Early term: 37 to 38 weeks
- Full term: 39 to 40 weeks
- Late term: 41 weeks
- Post-term: 42 weeks and beyond
It’s more helpful to see your due date as the middle of a window than as a deadline. Whether it’s your first pregnancy, your cycle length, your health and your baby’s growth can all affect when labour starts.
Pregnancy Weeks and Trimesters
- First trimester (weeks 1 to 12): Your baby’s organs begin forming. Nausea, fatigue and breast tenderness are common.
- Second trimester (weeks 13 to 26): Many women feel their best here. Energy often returns, and you may feel the first movements.
- Third trimester (weeks 27 to 40): Your baby gains weight quickly while you get ready for birth. Back, hip and pelvic aches are common.
Sources draw these boundaries slightly differently, so treat the weeks as a guide.
What to Do Once You Have Your Due Date
- Book your first prenatal visit. Your provider will confirm your dates and may schedule an early scan.
- Record your key dates. Keep your LMP, cycle length and due date handy for appointments.
- Plan your tests and scans. Many are timed by gestational week, so an accurate date matters.
- Look after yourself. Eat well, rest, drink enough water and take any supplements your doctor advises. Walking or prenatal yoga can help if your doctor says it’s safe for you.
- Prepare gradually. Sort out maternity leave, pack a hospital bag and line up support for after the birth.
Final Thoughts
A due date calculator is a quick, useful starting point, but the result is still an estimate. Use it to plan, stay flexible and have your provider confirm the date with an ultrasound. Ready to try it? Enter your details in the calculator above to see your estimated due date and how far along you are.
This article is for general information only and isn’t a substitute for professional medical advice. Please speak to your doctor or midwife about your pregnancy.
Frequently Asked Questions
How accurate is a due date calculator?
A standard due date calculator is typically accurate to within one to two weeks. That’s true if your cycles run regular and you know your LMP. First-trimester ultrasound narrows that window to about five to seven days.
Can my due date change during pregnancy?
Yes, and it’s common. A provider may adjust your date after a first-trimester ultrasound. This happens if it disagrees with your LMP-based estimate by more than five to seven days.
How is a due date calculated for IVF pregnancies?
Doctors calculate IVF due dates from the embryo transfer or retrieval date, not the LMP. Providers typically add 266 days for a fresh transfer, 263 days for a day-3 transfer, or 261 days for a day-5 blastocyst transfer.
What if I don’t know my last period date?
That’s common and not a problem. A first-trimester ultrasound can estimate your due date within about five to seven days by measuring the embryo directly.
How many weeks pregnant am I if I know my due date?
Count backward 40 weeks from your due date to find when your pregnancy started. Or count forward from your LMP if you know it.
Is a due date the same as a delivery date?
No. A normal, healthy birth can happen any time from 37 to 42 weeks. Fewer than 1 in 20 babies arrive exactly on their calculated due date.