When Do Babies Become Left or Right Handed?
Around 90% of adults are right handed, but no baby is born that way. Newborns start out with equal ability on both sides, and it takes years, not months, for a clear preference to properly settle.
Where hand preference comes from
The asymmetry between our left and right hands traces back to structural differences in the brain, and it starts remarkably early. Studies have found differences between the brain’s two hemispheres from as early as 29 weeks of pregnancy, and ultrasound scans show that many foetuses as young as 13 weeks already favour sucking their right thumb. One theory is simply about space. Around three quarters of babies spend their last weeks in the womb with their right arm free to move and their left arm tucked against their mother’s spine.
Genes clearly play a role too. Left-handed parents are more likely to have left-handed children, though only around half of the time, which tells us environment matters as well. Children often end up matching their mother’s handedness in particular, likely because they spend more early time observing and copying her.
How preference develops over time
- Birth to a few months: both sides should move equally. If you notice a strong, consistent preference for one side very early on, it is worth mentioning to your health visitor, as this can occasionally indicate something needing a closer look
- 4 to 6 months: babies may start holding a toy slightly longer in one hand than the other
- 6 to 9 months: a clearer preference for reaching with one hand, usually the right, starts to emerge in most babies, though they will still use their other hand plenty
- After 18 months: hand preference becomes more consistent, though it can still switch back and forth as children refine skills on both sides
- Around 4 years: most children have settled on a preferred hand, though for some this does not happen until as late as seven
Why this matters for development
Handedness is closely linked to how the brain organises itself, particularly around language. In right-handed people, language is usually processed mainly in the left side of the brain, and in left-handed people this is often reversed. This is a good reminder that small physical patterns, like which hand reaches first, are outward signs of much bigger things happening inside a developing brain.
There is no need to encourage one hand over another. Let your child’s preference emerge in its own time, and offer plenty of opportunities to use both hands freely through play.
Baby College classes are designed to give children rich, varied movement and hand use opportunities at every stage, supporting whichever pattern of development is right for your child.
