Pregnancy Calculator

Free Pregnancy Calculator - Track Your Due Date and Weeks

This pregnancy calculator gives you an estimated due date and tracks exactly how many weeks and days pregnant you are, right now, based on the date you enter. You can calculate it from your last menstrual period (LMP), an estimated conception date, or an IVF embryo transfer date — whichever one you actually know.

Along with the due date, this tool shows your current trimester, a full progress bar, an estimated conception date, and a week-by-week list of key pregnancy milestones with real calendar dates attached — no vague 'week 20' with no idea what date that actually falls on. Everything updates instantly as you change the date or method, no signup or app download needed.

How Pregnancy Due Dates Are Actually Calculated

Most people assume pregnancy is measured from the day of conception, but doctors and midwives actually count it from the first day of your last menstrual period (LMP), not conception. This might feel odd since you're not actually pregnant yet on that date, but it's used because the exact conception date is rarely known for certain, while the start of your last period usually is.

The standard method is called Naegele's Rule, named after the German doctor who popularized it in the 1800s: take the first day of your LMP and add 280 days, which is 40 weeks. That's your estimated due date. Because this calculator also lets you adjust for cycle length, it fine-tunes the estimate if your cycles run longer or shorter than the typical 28 days, since a longer cycle usually means ovulation — and conception — happens later than day 14.

Calculating by Conception Date or IVF Transfer

If you know your actual conception date — for example, from ovulation tracking or a single instance of intercourse — this calculator adds 266 days (38 weeks) instead of 280, since conception typically happens about two weeks after LMP in an average cycle.

For IVF pregnancies, the due date math is even more precise because the embryo's exact age is known at transfer. A Day 5 blastocyst transfer adds 261 days from the transfer date, and a Day 3 embryo transfer adds 263 days — both landing on the same estimated due date you'd get counting from LMP, just calculated from a more certain starting point.

Understanding Gestational Age: Weeks and Days

When someone says '20 weeks pregnant,' that's gestational age — the time counted from LMP, not from conception. So at the moment of a positive pregnancy test, you're already considered about 4 weeks pregnant even though the embryo itself is only about 2 weeks old. This can be confusing the first time you hear it, but it's the standard every doctor, app, and calculator uses, including this one.

This calculator shows gestational age as both a running week-and-day count (like '18 weeks, 3 days') and as a percentage of the full 280-day pregnancy, so you can see your progress at a glance no matter how you prefer to think about it.

The Three Trimesters, Explained Simply

Pregnancy is split into three trimesters, and this calculator automatically tells you which one you're in based on your current week.

• First Trimester (weeks 1-12): Early development, the highest miscarriage risk window, and often the toughest for morning sickness and fatigue.
• Second Trimester (weeks 13-27): Often called the 'easier' stretch — energy tends to return, and this is when most people find out the baby's sex and feel first movements.
• Third Trimester (weeks 28-40+): Rapid growth, more frequent checkups, and final preparation for labor and delivery.

Key Pregnancy Milestones This Calculator Tracks

Beyond the due date, this calculator maps out real calendar dates for the milestones that matter most through pregnancy: the estimated conception date, the typical first prenatal visit window, the end of the first trimester (when miscarriage risk drops significantly), the mid-pregnancy anatomy scan window, the viability milestone around week 24, the start of the third trimester, the point where a baby is considered full term (week 37), the due date itself (week 40), and the post-term marker at week 42 where providers often discuss induction.

Seeing these as actual dates on a calendar — not just week numbers — makes it much easier to plan prenatal appointments, maternity leave, and travel around each stage of the pregnancy.

How Accurate Is a Due Date Estimate?

It's important to set the right expectation here: a due date is an estimate, not a guarantee. Statistically, only about 5% of babies are actually born on their exact calculated due date. Most healthy, full-term births happen anywhere within about two weeks before or after the estimated date, which is completely normal.

Ultrasound dating done in the first trimester is generally considered the most accurate method available, often within 3-5 days, because early fetal measurements are very consistent across pregnancies. LMP-based dating is accurate for people with regular, well-remembered cycles, but becomes less reliable with irregular cycles — which is exactly why doctors often adjust the estimate after an early ultrasound.

LMP Method vs Conception Method vs IVF Dating

The LMP method is the most commonly used because it only requires knowing when your last period started, which most people track anyway. It assumes ovulation happened around day 14 of your cycle, adjusted here for your actual average cycle length.

The conception method is more precise if you know your conception date for certain, such as from ovulation testing or fertility tracking, since it removes the guesswork around when ovulation actually occurred. IVF dating is the most exact of all three, because the embryo's age is medically documented down to the day at transfer — which is why fertility clinics rely on it rather than LMP for IVF pregnancies.

Common Mistakes People Make With Due Date Calculators

A few mix-ups come up again and again, so it helps to know them ahead of time.

• Confusing conception date with LMP date — they're about two weeks apart and give very different due dates if swapped by mistake.
• Assuming irregular cycles won't affect accuracy — they can shift the real ovulation date well away from the standard day-14 assumption.
• Treating the due date as a hard deadline instead of a window — normal, healthy births happen anywhere from about week 37 to week 42.
• Not updating the estimate after a first-trimester ultrasound, which is usually more accurate than LMP-based dating alone.
• Forgetting that gestational age counts from LMP, not conception, which is why 'week 4' can feel confusingly early compared to when conception likely happened.

Who This Pregnancy Calculator Is For

This tool is built for anyone who wants a clear, instant estimate — someone who just found out they're expecting and wants to know their due date, someone tracking IVF transfer dates from a fertility clinic, or anyone simply curious how far along a pregnancy is and what's coming up next on the calendar.

This calculator is for general informational tracking only and does not replace medical care. Due dates, viability windows, and milestone timing can vary based on individual health factors, and only a doctor or midwife using clinical exams and ultrasound measurements can give a medically confirmed due date. Anyone who is pregnant or trying to conceive should be under the care of a qualified healthcare provider throughout.