When to Lower a Crib Mattress (and When to Move to a Toddler Bed)
Three physical milestones tell you it’s time — not your baby’s age on a calendar.
The short answer for when to lower crib mattress height: drop it the moment your baby can sit unassisted or push up on hands and knees, typically around 5–6 months, and move it to the lowest setting as soon as they can pull to stand, typically around 9 months. The switch from crib to toddler bed is a separate decision, guided by the American Academy of Pediatrics’ benchmark of about 35 inches tall or a crib rail that sits below your child’s chest — whichever comes first.
When to lower crib mattress height: the 3 milestones to watch
- Sitting unassisted or pushing up on hands and knees (around 5–6 months). This is your first cue to drop the mattress from the highest newborn setting to the middle position. A baby who can push their torso up can also push themselves over a mattress that’s still sitting high.
- Pulling to a stand (around 9 months). Move the mattress to the lowest setting immediately — don’t wait for a specific age. Once a baby can pull up on the rail, a mattress at the middle height puts the rail dangerously close to tip-over range.
- Reaching about 35″–36″ tall, regardless of mobility stage. Height alone is a trigger even if your child hasn’t hit the earlier milestones on schedule — some toddlers get tall before they get climby.
When to transition from a crib to a toddler bed
Lowering the mattress buys you time, but it’s not a permanent fix — at some point the crib itself needs to go. The American Academy of Pediatrics recommends transitioning to a toddler bed once your child reaches about 35 inches tall, or once the crib rail sits below their chest while standing, since at that height a child can climb out on their own and risk a fall. The AAP also generally advises against moving a child out of a crib before 18 months, even if they’re tall for their age, since younger toddlers usually aren’t developmentally ready to stay safely in an open bed. Between those two guardrails, the actual timing comes down to your individual child’s size, climbing attempts, and temperament — there’s no single correct age. For the full guidance, see the American Academy of Pediatrics’ guidance on toddler bed timing.
If you’re shopping for a crib that can grow with your child longer, several convertible mini cribs handle this transition without a separate furniture purchase — see our picks for the best mini cribs for small spaces, most of which convert to a toddler bed or daybed with an add-on kit. Bookmark this page and revisit it every few months — knowing when to lower crib mattress height is really just a matter of checking these milestones as your child grows.