Pregnancy Due Date Calculator

The Science of Predicting Birth

Finding out you are pregnant is one of life's biggest moments, followed immediately by the question: "When is the baby coming?"

While nature operates on its own schedule, medical professionals use a standardized method called Naegele's Rule to predict your delivery window. This formula, developed by German obstetrician Franz Naegele in 1812, calculates your Estimated Due Date (EDD) based on the first day of your Last Menstrual Period (LMP).

Our calculator uses this rule but adds a layer of precision by adjusting for your personal Cycle Length, offering a more tailored prediction than generic charts.

The "Phantom" Two Weeks

One concept that confuses almost every new parent is the "Gestational Age" vs. "Fetal Age."

If your doctor says you are 6 weeks pregnant, your baby has only actually existed for about 4 weeks. How is that possible?

The math explained: Pregnancy dating starts from the first day of your last period (LMP). However, you don't actually conceive until you ovulate, which happens roughly 14 days after your period starts. The medical community counts those first two weeks (before you were even pregnant) as part of the 40-week timeline to standardize calculations.

What if my periods are irregular?

Standard due date calculators assume a "perfect" 28-day cycle, with ovulation happening exactly on Day 14.

However, if your cycle is shorter (e.g., 24 days) or longer (e.g., 35 days), your ovulation day shifts. This means the baby was conceived earlier or later than the standard math assumes.

• Short Cycles: You likely ovulated earlier, meaning your due date might be sooner.
• Long Cycles: You likely ovulated later, meaning your due date might be later.

Our calculator allows you to input your average cycle length to account for this shift automatically.

Accuracy: Is the Due Date a Guarantee?

No. It is an Estimate, not a deadline. In reality, only about 4-5% of babies are born on their exact due date.

Why Your Doctor Might Change Your Date

You might use this calculator and get a date of January 1st, but then go for your first ultrasound and the doctor changes it to January 5th. Who is right?

Trust the Ultrasound.

In the first trimester (usually between 8 and 12 weeks), doctors perform a "Dating Scan." They measure the baby from head to rump (Crown-Rump Length). Because all embryos grow at almost the exact same rate during the first few weeks, this measurement is highly accurate. If the scan date differs from your LMP date by more than 7 days, doctors will usually update your official due date to match the scan.

The Three Trimesters Explained

Pregnancy is divided into three distinct stages. Knowing when they start helps you plan for symptoms and medical checkups.

Diet & Nutrition During Pregnancy

The phrase "Eating for Two" is a myth. You only need about 300-500 extra calories per day, and only in the second and third trimesters.

However, what you eat matters more than ever. You need increased protein for tissue growth and must be careful with stimulants.

• Caffeine: Doctors generally recommend limiting caffeine to under 200mg per day (roughly one 12oz cup of coffee). Use our Caffeine Calculator to stay safe.
• Protein: Aim for at least 70g-100g of protein daily to support fetal growth. Check your intake with our Protein Calculator.
• Hydration: Blood volume increases by up to 50% during pregnancy, meaning you need significantly more water.