Should I wake my baby up from a 3 hr nap?

What the evidence says

It depends a lot on your baby's age. The Canadian Paediatric Society notes that napping needs vary hugely between babies, some cat-nap for 20 minutes while others sleep 3 or more hours at a stretch, and newborns can sleep 3 to 4 hours at a time as part of up to 18 hours of sleep a day. So a 3-hour nap by itself is not unusual or worrying.

For newborns in the first few weeks, the main reason to wake a baby is feeding, not sleep timing. Health guidance says babies typically need to eat every 2 to 4 hours in the early weeks, and you may need to wake a very sleepy newborn to feed, especially if they're not yet back to birth weight or gaining well. Once feeding and weight gain are well established, an Australian parenting guide notes that unless your doctor says otherwise, there's usually no need to wake a baby just for a feed, and an occasional extra-long sleep is fine.

For older infants and toddlers, the picture is a bit different. Smaller studies using activity monitors have found that longer or later naps are linked to later bedtimes and shorter nighttime sleep, though this evidence is observational and lower quality rather than from controlled trials. If your baby is over about 6 months and a long afternoon nap seems to be pushing bedtime very late or causing nighttime awakenings, gently capping nap length or nap timing earlier in the day may help, but there's no strict rule.

If your baby seems unusually hard to wake, floppy, feeding poorly, or not producing normal wet diapers, contact your doctor rather than relying on general nap advice.