At what age is the WHO-GMM used for a child?

A handy ruler for the early walking years — the WHO-GMM tells us the typical age range in which a child reaches each big motor milestone.

In short

The WHO Windows of Achievement for Gross Motor Milestones (WHO-GMM) is used for infants and young children, roughly from 4 months to about 24 months (2 years) of age. It maps the typical age window in which most healthy children reach six key gross-motor milestones — sitting, standing, crawling and the early steps of walking. It is a reassuring reference for the early movement years, not a test that continues into the school years.

What the WHO-GMM covers and when

The WHO-GMM describes six gross-motor milestones, each with a window — an early-to-late age range rather than a single deadline — that reflects how much healthy variation is normal between babies. In broad terms these windows span:

• Sitting without support — from around 4 months
• Hands-and-knees crawling — from around 5–6 months
• Standing with assistance — from around 5–6 months
• Walking with assistance — from around 6 months
• Standing alone — from around 7 months
• Walking alone — typically by around 18 months, with the window extending towards 18–24 months

Because each milestone has a window, a baby who sits or walks a little earlier or later than a friend is usually still developing perfectly well. The WHO-GMM simply helps families and clinicians notice when a milestone falls outside its expected window, which is a gentle prompt for a closer look — never an automatic concern on its own.

When a review helps

Consider a developmental review if your child has clearly passed the later edge of a window without reaching that milestone — for example, not sitting independently well beyond the sitting window, or not walking by around 18 months — or if you notice stiffness, floppiness, or one side of the body being used much less than the other. Early observation protects a child's movement, confidence and play.

The Pinnacle way

This is general information, not a diagnosis — a clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care, never from an app or form. Our team uses references like the WHO-GMM alongside a full developmental picture, then shapes any helpful support, which may include occupational therapy for movement and play skills.

Trusted sources

WHO Multicentre Growth Reference Study, which established the Windows of Achievement for the six gross-motor milestones; WHO Nurturing Care Framework on early childhood development; CDC and AAP/HealthyChildren guidance on motor milestones.

Next step — If your child is in the early walking years and you'd like reassurance about their movement milestones, book a developmental review to map their progress against the expected windows.