About this site
What it is, and what it is not.
19 September 2026
Why it exists
This site was built by a parent, for their own use.
The questions that come up most often while raising a small child are very concrete: what should they be eating this month, what is worth practising, is the height and weight normal, when is the next vaccine. All of these have established answers, and those answers are written down in WHO and national health guidance. But those documents are written for professionals, not for someone holding a baby at two in the morning.
What is missing is not the knowledge. It is the knowledge reorganised around one question: how old is this child right now. That is what this site does.
Where the content comes from
Nothing here is an original medical opinion. It is a reorganisation of published authoritative material. The main sources:
WHO Child Growth Standards (2006) and the Growth Reference for 5-19 years (2007). Every curve and percentile on this site is computed from WHO's own published LMS parameter tables, taken directly from who.int and used without adjustment.
China's Dietary Guidelines for Residents (2022), infant, young child and preschool sections — the basis for the feeding guidance and the food introduction timeline.
China's National Immunization Program schedule (2021) — the basis for the vaccination timetable.
CDC developmental milestones (2022 revision) — the main reference for milestones. One important feature of that revision is the shift from what 50% of children can do to what 75% can do, specifically to reduce watchful waiting and encourage earlier screening.
Plus relevant paediatric consensus statements, guidelines and research.
How the percentiles are calculated
If you want to verify it: WHO publishes its growth standards as LMS parameters — skewness, median and coefficient of variation. For a given age and sex, the z-score of a measurement is z = ((X/M)^L − 1) / (L·S), with the logarithmic form used when L is zero. The percentile is the cumulative standard normal probability of that z-score.
This site uses WHO's day-by-day expanded tables, sampled monthly. Months 0-60 come from the 2006 Child Growth Standards, months 61-72 from the 2007 Growth Reference. Head circumference stops at 60 months because WHO publishes no reference beyond that age.
The 0.7cm step at 24 months, where measurement switches from recumbent length to standing height, is preserved rather than smoothed. It is a genuine difference in how the measurement is taken.
What it cannot do
It does not know your child. Everything here is a population statistic and applies to no individual in particular.
It cannot diagnose. The 'when to see a doctor' section on every page exists to send you to one, not to stand in for one.
It cannot guarantee currency. Guidelines are revised and local practice differs, vaccination schedules most of all. Your official immunisation record is the authority.
It has no clinical team behind it. Saying so plainly is worth more than inventing an advisory board. You should know what you are reading, and when you need to go and find an actual professional.
About your data
No accounts, no backend, no analytics. The birthday and measurements you enter stay in your browser. See the Privacy Policy.
This is not a marketing claim but a description of how the site is built: static pages plus arithmetic running in your browser.
If you find an error
If anything here is wrong, out of date, or inconsistent with the rules where you live, please write: hi@ppily.com
With health content, one error can matter a great deal. Pointing one out is the most valuable contribution anyone can make to this site.
The English and Chinese versions of this page carry the same content.