How fast do kids' feet grow?

The pace by age, in round numbers: under two, a size about every four months, three sizes a year. Two to four, about every five months. Four to six, about every six. From school age the pace eases to a size every eight to ten months. The numbers are deliberately round; anything sharper would be false precision about an average child who does not exist.

This is why the shoe shelf, and never the shirt drawer, is where the money goes in the early years: shoes at toddler pace are replaced three times a year, and unlike a slightly short sleeve, a slightly short shoe does harm. It is also why hand-me-down shoes between siblings so rarely line up; by the time the younger one reaches the size, the season is wrong.

The foot does not complain

Do not wait for the child to say the shoes are tight, because most never do. A young foot is soft cartilage; it folds into the shoe it is given and the toes curl without a word. The complaint arrives months later as red pressure marks and worn toenails. Measuring is the only input worth trusting: in the evening, against a wall, longest toe, plus 10 to 15 mm.

One more honesty: growth arrives in bursts. A foot can hold still for a quarter and then take a size in six weeks, summer being a favorite. The rates above predict the average path; the tape measure decides the actual one. Under four, measure every other month; older, quarterly, and always before the season's big buy.

These curves are the model our app runs per child: it knows the sizes in the wardrobe and when they changed, and says when the next size is probably due, in time to buy calmly instead of urgently. The word is probably; the measurement settles it.