By 6 months, two-thirds sleep through much of the night.
Starting at 3 months of age, many babies start sleeping for longer stretches at night — anywhere from 4 to 6 hours — although this varies from infant to infant. By 6 months, two-thirds sleep through much of the night. Babies that are smaller at birth start to sleep for longer stretches when they are closer to 12 to 13 pounds.