About this site

What this site is

Wonder Weeks Calculator is a free web tool for parents of babies and toddlers up to about twenty months. You enter a due date or birth date and get a personal calendar that marks ten estimated fussy windows, along with a short explanation of each one. The site also offers a baby temperament check and the longer leap guides linked at the bottom of every page.

The calculator is available in many languages. The leap guides, FAQ and information pages are currently written in English.

Who runs it

The site is run by a small independent operator, referred to on this site as the Wonder Weeks Calculator operator. The same operator runs a separate Korean-language service at wonderweeks.kr, which Korean-speaking visitors are directed to. We are not a medical provider and are not affiliated with the authors or publishers of The Wonder Weeks book or app.

You can reach the operator at mail@llkr.kr.

How the guides are written

The leap guides describe general, widely accepted information about infant development, sleep, feeding and safety, organised around the timing that the calculator uses. They are written for this site and are reviewed against the guidance commonly given by public health services and paediatric organisations, such as safe-sleep advice, the usual timing for starting solid food and standard warning signs of illness.

We avoid precise medical claims and do not recommend treatments or products. Where babies vary, we say so. If you notice an error or something that is unclear, please tell us through the contact page and we will review it.

What the site cannot do

Nothing on this site is a diagnosis or a substitute for advice from a doctor, nurse, midwife or health visitor who knows your child. Dates are estimates, and a fussy window never explains away signs of illness. If you are worried about your baby, contact a health professional.

Advertising and costs

The site is free to use. Some content pages, such as these guides, display advertising from Google AdSense to help pay for hosting and development. The calculator screens themselves do not show ads. Advertising does not influence what we write in the guides.