Calculators for parents

Ten free calculators for parents: clothing and shoe sizes, WHO growth percentiles, sleep schedules, weaning, due date and child age. Everything runs in your browser — no account, no data sent to a server.

Before birth

Due dateWeeks so far, the due date and the 37–42 week birth window.OvulationOvulation and the fertile window for three cycles, on a calendar.

Sizes

Clothing sizeHeight and build → EU/US/UK size with a range and a fit tip.Shoe sizeFoot length → target insole length and size: precise, not “to grow into”.Bike sizeHeight → 12–24″ wheels or a balance bike, with a fit check.

Growth & development

Growth percentilesWHO growth curves: where your child sits among peers, with your own measurements.Height predictorPredicted adult height from the parents’ heights, with an honest range.Child ageExact age in years, months and days plus upcoming milestones.Corrected ageCorrected age for a preterm baby and the gap to term.

Sleep & food

Sleep scheduleWake windows by age and a sample day as a ribbon.Weaning planner“Not before” age guides by food group — no doses, no volumes.

Lists & packing

Hospital bagHospital bag for mum and baby: packed by week 36.Kindergarten checklistEverything for kindergarten, tickable: indoor shoes, spares, outdoor gear.School checklistThe school list with checkmarks — and what the first-grader basket costs.Travel checklistDocuments, carry-on and the road — forget nothing on holiday.

Every tool is free and needs no account. Your child’s data stays in your browser — we never receive it.

Browse the catalog →

Why we built these

We run a shop for children’s things and keep meeting the same parental questions: which size to take when a child is between sizes; whether it is fine to be shorter than peers; when the boots stop fitting; what a seven-month-old may already eat. Those questions are answered by arithmetic and open data rather than marketing copy — so we turned them into separate calculators and opened them to everyone.

Where an official standard exists, we follow it: growth percentiles are built on the WHO tables (Child Growth Standards 2006 and Growth Reference 2007), and European clothing sizes are based on height in centimetres per EN 13402. Where there is no single standard — sleep norms or weaning timing, for example — we say plainly that these are widely used guides, not prescriptions.

One profile across all tools

What you enter — sex, date of birth or age, height, weight, foot length — is stored in your browser and filled into the other calculators. Check the percentiles and the clothing calculator already knows the height; calculate a due date and the corrected-age tool picks it up. The profile can be deleted with one button in the line above the form.

We deliberately do not ask for registration: a tool should work immediately, and a child’s data is safer on your device than on our server.

Frequently asked questions

Are the calculators paid?

No. All ten tools are free, need no account and have no limit on the number of calculations.

Where does my child’s data go?

Nowhere. The maths happens in your browser and the profile lives in your device’s local storage. We never receive the name, the date of birth or the measurements.

How much can I trust the result?

These are reference calculations, not a medical opinion. Percentiles and sizes follow official tables, but any question about your child’s health, development or nutrition belongs to a paediatrician.

Can I print or save the result?

Yes. Every result has a “Print” button — you get a clean sheet without the site chrome — and “Save as image”, handy for sending the result to a family chat.