One day your baby is sleeping constantly and you cannot figure out why, and then you realise they have grown an inch since last week. Growth spurts are real, they are dramatic, and they can genuinely catch you off guard if you do not know what to look for. Baby growth spurts happen at fairly predictable times: around 2 to 3 weeks, 6 weeks, 3 months, 6 months, and 9 months, though every baby is different. The signs are usually pretty obvious once you know what they are. Sudden increase in hunger is the most common sign: a baby who was feeding every 3 hours suddenly wants to feed every hour or even more. This is called cluster feeding and it is normal and purposeful. It signals your body to produce more milk to meet the new demand. Increased fussiness and crying even when all obvious needs are met. Wanting to be held constantly and only settling when in arms. Sleeping more than usual or conversely fighting sleep and seeming unable to settle. Seeming hungrier than normal even after a full feed. Growth spurts typically last 2 to 7 days. The best thing to do is respond to your baby cues: feed on demand, hold them as much as you need to, rest when you can. For formula-fed babies you may need to increase the amount offered per feed temporarily. This too shall pass.