Labor timing calculator
- Why the labor forecast changes every day you remain pregnant
The forecast is recalculated from today forward each time it runs. Why the window moves later and narrows while the due date stays fixed.
- Does a previous early or late birth predict this one
What the research shows about the relationship between the timing of one birth and the next, and how the calculator translates it into a small shift.
- The chance of labor each week from 37 to 42 weeks
Week-by-week probabilities of spontaneous labor from the calculator's baseline model, and the difference between a week's share and the chance if labor has not yet begun.
- What the 50% labor window means
The labor calculator's main result is a date range containing half of the remaining probability. How the range is calculated, why it changes, and how to read it.
Due date and pregnancy week calculator
- How accurate a first-trimester ultrasound is for dating
Crown-rump length dating before 14 weeks has an error of about five to seven days. Where the error comes from and when the scan overrides the period date.
- LMP, ultrasound, ovulation, and IVF dating, and which takes priority
The arithmetic behind each method of estimating a due date, the accuracy of each, and the priority order used when they disagree.
- How pregnancy weeks are counted
Gestational age is counted from the last menstrual period, about two weeks before conception. What "24 weeks 3 days" means and how weeks map to months and trimesters.
- Why a due date is a midpoint rather than a deadline
A due date is day 280 of a range more than five weeks wide. What the date is used for, how it is established, and why most births do not occur on it.
Child growth planner
- How the planner predicts clothing and car-seat sizing from growth
Clothing limits come from brand charts and car-seat limits from manufacturer manuals. How the planner combines them with a growth projection to give a re-check date.
- What a growth-velocity estimate can and cannot tell you
The planner's date ranges come from WHO growth-increment distributions in infancy and from growth-channel scenarios later. What those ranges are and are not.
- WHO and CDC growth charts, and which one the planner uses
The WHO standard describes growth under favorable conditions; the CDC reference describes how U.S. children grew. Why the planner switches between them at age 2.
- How growth percentiles work and when a change in percentile matters
A percentile compares a child with a reference population at one age. What the number means, how the reference charts were built, and when a change is significant.
Child height predictor
- Sitting height, leg length, and what the NHANES III model adds
Car-seat head clearance depends on seated height, not standing height. How the planner's sitting-height reference was built from NHANES III and what it does not claim.
- Growth spurts and puberty timing, and why the prediction widens in adolescence
The pubertal growth spurt varies by two years or more between children of the same age. Why adult-height prediction is least accurate in early adolescence.
- Why a two-year-old's height percentile only loosely predicts adult height
Height at age 2 is correlated with adult height, but the prediction error is 4 to 5 cm or more. Why projecting a percentile to adulthood is unreliable.
- Mid-parental height: the formula, its error range, and its limits
The parent-average height formula has an error range of about 10 cm in either direction. What it can indicate, and why the predictor reports a different estimate first.
Hospital bag checklist
- A hospital bag timeline keyed to the labor forecast
The labor calculator's 10% date gives a defensible packing deadline. How to read it, what it is at each week, and how the checklist and the Labor-Ready Plan use it.
- What hospitals provide, and what people over-pack
Facilities differ in what they supply for labor, recovery, and the baby. The items most often reported as unused, and the one question that settles most of them.
How the calculators are built
- Reading a probability calculator without misreading it
A result from any calculator on this site is a population estimate conditioned on a few answers. The common misreadings, and what each figure does and does not say.
- How My Baby ETA turns a published study into a calculator
The rules used to select sources, adapt their estimates for a consumer form, and identify which values are calibration choices rather than reported results.