Categories
Calculators & Tools
How the calculators work — the formulas, the sources, and what the numbers mean.
Baby Zodiac Signs by Due Date: What Sign Will Your Baby Be?
Your due date lands your baby in one of 12 zodiac signs — until it moves. Here are the exact date ranges our calculator uses, the cusp windows where two signs are still in play, and why an estimated date can change the answer.
BMI Before Pregnancy: Why It Matters and What It Changes
Your pre-pregnancy BMI is the input that sets your recommended weight gain, and it follows you through the whole pregnancy. Here's how the BMI bands map to the IOM targets, and where a single height-and-weight number stops being useful.
How Due Date Calculators Work (And Why They're Just Estimates)
Most people who Google "due date calculator" want their EDD in 10 seconds. Here's what's actually happening when you punch in a date — and why your provider's first-trimester ultrasound is the only date that really counts.
Pregnancy Weight Gain: How Much Is Right for You (IOM Targets by BMI)
There is no single right number for pregnancy weight gain — there are four, and the one that applies to you depends on your BMI before you conceived. Here are the IOM 2009 ranges, the weekly rates behind them, the separate twin numbers, and what the evidence actually says about gaining more or less.
The Chinese Gender Predictor: Fun Tradition or Real Science?
The Chinese gender chart turns two numbers — lunar age and lunar conception month — into a boy-or-girl answer. Two large studies say it lands at chance. Here is the real math, and the two tests that actually tell you.
The Mayan Gender Predictor: How It Works and Whether It Is Accurate
The Mayan gender predictor compares the mother's age at conception with the month she conceived, then calls boy or girl on whether both numbers share the same parity. Here is the arithmetic, the folklore behind it, and what actually determines your baby's sex.
When Did I Conceive? Reverse Due Date and Conception Date Explained
Subtract 266 days from your estimated due date and you have your most likely conception date. Here is why that number is 266 and not 280, why conception means ovulation rather than the night you remember, and how wide the honest answer really is.