How is the due date calculated for IVF pregnancies?

For IVF the due date is very accurate because the embryo age is known. For a Day 5 (blastocyst) transfer the due date is 261 days from the transfer date; for a Day 3 transfer it is 263 days. This calculator handles both when you choose the IVF method.

What is the difference between conception date and last period?

Your last menstrual period (LMP) is the first day of your most recent period and is used as the official start of pregnancy. Conception usually happens about 2 weeks later at ovulation. Because most people know their LMP but not the exact day of conception, the LMP method is the standard one used by doctors and midwives.

🤰 Pregnancy

Pregnancy Calculator 2026

Work out your due date, exactly how many weeks and days pregnant you are, your trimester, estimated conception date and a full week-by-week breakdown with baby size, milestones and appointments. Calculate from your last period, conception date, due date or IVF transfer.

Calculate from

First day of your last menstrual period

The first day of your most recent period (LMP)

Embryo transfer day

Day 5 is a blastocyst transfer, Day 3 is a cleavage-stage transfer

Calculate as of

Defaults to today — change it to check a past or future date

Average cycle length (optional)

Only used with the last-period method. Default is 28 days.

You are

Enter a date to see your pregnancy details

📅 How far along --

🌸 Current trimester --

🎯 Estimated due date --

🍼 Estimated conception date --

⏳ Days remaining --

🎂 Baby's zodiac sign --

➡️ Next milestone --

📖 Week-by-Week Breakdown

Your current week is highlighted after you calculate. Sizes are approximate averages — every baby grows at its own pace.

Week	Size of	Length	Weight	What's happening

1st trimester 2nd trimester 3rd trimester

📋 The Three Trimesters at a Glance

Pregnancy is counted as 40 weeks from the first day of your last period.
Trimester	Weeks	Roughly
First trimester	Week 1 – 13	Months 1–3
Second trimester	Week 14 – 27	Months 4–6
Third trimester	Week 28 – birth	Months 7–9

🍼 What to Expect in Each Trimester

🌱 First trimester (weeks 1–13)

The baby's major organs, brain and heartbeat develop. You may feel very tired and experience morning sickness, tender breasts and food aversions. This is the most important time to take folic acid and avoid alcohol and smoking.

🌸 Second trimester (weeks 14–27)

Often called the "honeymoon" phase — sickness usually eases and energy returns. You'll likely feel the first baby movements, start to show, and can find out the baby's sex at the mid-pregnancy scan around week 20.

🤰 Third trimester (weeks 28–40)

The baby gains weight quickly and gets into position for birth. You may have backache, heartburn, swelling and trouble sleeping. Antenatal visits become more frequent as you get ready to meet your baby.

📌 Key Milestones & Appointments

🫀 Heartbeat detectable~ Week 6

🩺 Dating / booking scanWeeks 8–14

🧬 NT scan / screeningWeeks 11–14

🌸 Second trimester beginsWeek 14

👶 First movements ("quickening")Weeks 16–22

🖼️ Anomaly / 20-week scanWeeks 18–21

🍬 Glucose (gestational diabetes) testWeeks 24–28

🤰 Third trimester beginsWeek 28

💉 Whooping cough vaccineWeeks 16–32

�� Considered full termWeek 37

🎯 Estimated due dateWeek 40

How Does This Pregnancy Calculator Work?

A full-term pregnancy lasts about 40 weeks, counted from the first day of your last menstrual period (LMP). This calculator gives you four ways to work that out: from your last period, your conception date, a known due date, or an IVF transfer date. From there it calculates exactly how many weeks and days pregnant you are, which trimester you're in, your estimated conception and due dates, and a full week-by-week view of your baby's growth.

Why am I "2 weeks pregnant" at conception?

Because pregnancy is dated from your last period, not from conception. Ovulation and conception usually happen around 2 weeks after your period starts, so by the time the baby is actually conceived you are already counted as roughly 2 weeks pregnant. This is the standard "gestational age" that doctors and midwives use everywhere.

How accurate is the due date?

A due date is an estimate, not a deadline. Naegele's rule adds 280 days to the first day of your last period. If your cycles are longer or shorter than 28 days, your due date shifts slightly, which is why you can enter your cycle length. Only about 1 in 20 babies arrive on the exact due date — most come within two weeks either side. A first-trimester dating ultrasound is the most accurate confirmation.

IVF due dates

IVF due dates are unusually precise because the exact age of the embryo is known. For a Day 5 blastocyst transfer the due date is 261 days after transfer; for a Day 3 embryo it's 263 days; for a Day 6 blastocyst it's 260 days. Choose the IVF method above and select your embryo day to use these exact figures.

Frequently Asked Questions

How does a pregnancy calculator work? +

It estimates your due date and current stage. The standard method counts 280 days (40 weeks) from the first day of your last period. You can also calculate from conception, a known due date, or an IVF transfer, and the calculator works out your weeks, trimester and week-by-week progress.

How many weeks pregnant am I? +

Pregnancy is measured from the first day of your last period, so at conception you're already about 2 weeks pregnant. This tool shows your exact weeks and days, e.g. 12 weeks and 3 days.

Is my due date exact? +

No — only about 5% of babies arrive on their due date. Most are born within two weeks before or after. A first-trimester scan is the most accurate way to confirm it.

How is the due date calculated for IVF? +

IVF due dates are very accurate. A Day 5 transfer is due 261 days later, a Day 3 transfer 263 days later, and a Day 6 transfer 260 days later. Choose the IVF method and your embryo day above.

Last period or conception date — which should I use? +

Use your last period (LMP) if you know it — that's the official medical method. Use conception only if you know the exact day (e.g. ovulation tracking or IVF). The LMP method is the standard used by doctors and midwives.

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Medical note: This calculator gives general estimates only and is not medical advice. Dates from a calculation can differ from a dating ultrasound — always follow the guidance of your own doctor or midwife.