Pregnancy Due Date
Calculator
Estimate your due date and track your pregnancy week by week
How it works
Most due dates are calculated using a simple guideline called Naegele’s rule: add 40 weeks (280 days) to the first day of your last menstrual period. It’s a helpful way to estimate timing, but it’s not a prediction — bodies and babies have their own schedules, and your care team may refine dates based on scans and your individual circumstances.
If you know a conception date, the estimate shifts slightly because pregnancy is typically dated as 38 weeks (266 days) from conception. For IVF, using the transfer date can be even clearer because the embryo age is known — this calculator uses a common estimate for a 5-day blastocyst transfer, but clinics may use different conventions depending on the transfer day and protocol.
Even with the best information, a due date is best thought of as a landmark on the calendar, not a deadline. Only a small percentage of babies arrive exactly on their estimated date, and that’s completely normal. Use this as a friendly guide for planning — and lean on your midwife or doctor for the most accurate dates and care.
Frequently asked questions
How accurate is a due date calculator?
Due date calculators give a helpful estimate, but they can’t predict the exact day your baby will arrive. Only around 5% of babies are born on their exact due date, and many arrive a little earlier or later. Your midwife or doctor may refine timing based on scans and your individual circumstances.
How is my due date calculated from my last period?
The most common method adds 40 weeks (280 days) to the first day of your last menstrual period. This is often called Naegele’s rule. It’s widely used because many people know their period date even if they don’t know the exact day of conception.
What's the difference between calculating from LMP, conception, or IVF transfer?
LMP uses an average cycle and adds 40 weeks, while conception-based estimates add 38 weeks from conception. IVF transfer can be clearer because the embryo age is known, but clinics may use slightly different conventions depending on the transfer day. If you’re unsure, use the date your clinic provides as your reference.
How many weeks pregnant am I?
This calculator shows your current pregnancy week and day (for example, 14 weeks and 3 days). Pregnancy is usually counted from the first day of your last period, so if you use conception or IVF dates, the tool converts them into an LMP-equivalent starting point to keep the week count consistent.
What trimester am I in?
Trimester timing can vary slightly by country and clinic, but a common approach is: 1st trimester up to 12 weeks, 2nd trimester from 13 to 26 weeks, and 3rd trimester from 27 weeks to birth. Your care team may describe these ranges a little differently, and that’s normal.
Can my due date change as my pregnancy progresses?
Yes — it can. Early ultrasound measurements sometimes suggest a slightly different due date than an LMP-based estimate, especially if cycles are irregular. If your care team updates your due date, it’s best to follow their guidance for appointments and planning.
When should I see a doctor or midwife to confirm my due date?
If you think you might be pregnant, it’s a good idea to book in with a midwife or doctor as soon as you feel ready. They can confirm pregnancy, talk you through next steps, and arrange dating scans when appropriate. If you have any worrying symptoms or feel unwell, seek medical advice promptly.