About howtallai

howtallai is a free height predictor with a set of growth reference tables. It is run by an independent developer, not by a clinic, hospital or public health agency, and it is not affiliated with or endorsed by the CDC, the WHO or any medical institution.

Why it exists

"How tall will my child be?" and "How tall will I be?" are common questions, and the honest answer is a range, not a number. The site was built to give that range for free, to show how it is calculated and where it can be wrong, and to put the official reference tables it relies on next to it. The estimate and its range are shown in full without an account.

Who runs it

One independent developer builds and maintains the calculator, the guides and the tables. The developer is not a medical professional, which is why the site states its sources and method in full and points to a pediatrician wherever a question needs one. The site does not sell supplements, devices or routines that claim to add height, and has no affiliate arrangements with anyone who does.

Where the data comes from

Children 2 to 20 years: CDC 2000 Growth Charts, stature-for-age (the file statage.csv).
Babies and toddlers under 2: WHO Child Growth Standards (2006), length-for-age tables by week (birth to 13 weeks) and by month (birth to 24 months).
Adults: NCHS, NHANES Anthropometric Reference Data, United States, August 2021–August 2023, Tables 7 and 8.

The values are read from the official files without interpolation. File names, rows used and every calculation are listed on the data and method page.

How the prediction is calculated

The calculator combines two estimates: the mid-parental target (the average of both parents' heights, plus 6.5 cm for a boy or minus 6.5 cm for a girl) and a projection of the child's current height using the share of adult height usually reached at that age. It blends the two and reports a range that is wider for younger children, when inputs are missing, and when the two estimates disagree. The exact weights and range rules are on the data and method page.

Published target-height methods land within 8.5 cm (3.3 in) of adult height for about 95% of people (Tanner et al., 1970). This calculator has not been checked against measured adult heights, so it makes no claim to be more accurate than any other method.

What this site is not

Not medical advice. Nothing here is a diagnosis or treatment, or a substitute for a pediatrician or family doctor.
Not a measurement. An estimate built on parents' heights cannot tell two siblings apart in advance, and remembered heights or doorframe measurements add error to the result.
Not a test for a growth problem. It cannot detect a medical cause of slow growth. If a child's growth worries you, speak to a pediatrician; the data and method page lists the patterns the site's guides flag.
Not for every age. The calculator is designed for roughly ages 8 to 20; the reference tables cover birth to adulthood.

How the site is kept up to date

The reference tables are fixed datasets and change only when CDC, WHO or NCHS publish a new version. The chart pages are rebuilt from stored copies of the official files, which are checked against fixed checksums on every rebuild. Errors reported by readers are checked against the source file and corrected when confirmed. This page was last reviewed on October 30, 2026.

Contact

Corrections, questions about the method, and privacy requests go to [email protected]. The contact page says what to include. What the calculator stores is described in the privacy policy.