When do babies laugh for the first time? she's 4 months old and smiles all the time.

Baby is well & happy: Smiling or laughing is a sign of content and in a baby, it suggests she is feeling well/happy. We don't really know exactly when baby purposefully smiles, but often by 2 months, baby interacts with others, cooing, giggling, smiling, and crying too. So, my guess is around 2 months, some may do earlier, some later. Congrats on the baby. Baby=miracle of life. Enjoy and good luck.

The average age is 4: Mos., but not all babies read the manual. Fake coughs & bronx cheers ("raspberries") are also 4 -month milestones. The important thing is that her smiling, cooing & gooing are socially reciprocal;i.E, she smiles & matches your high-pitched open-vowel sounds (ooh, aah) when you engage her. Put her in her own bed, drowsy but awake, to fall asleep before she develops implicit memory at 5 mos.