First rule: your artist outranks this guide
One thing before the timeline: your artist gave you aftercare instructions for your specific tattoo, skin and session, and those override anything you read here or anywhere else on the internet. This guide exists to explain what's normal and what isn't so you panic less; when it and your artist disagree, your artist wins. When something looks wrong, message them first; they've seen a thousand healing tattoos and yours for real.
What healing looks like, week by week
Days one to three: the tattoo is an open wound. It'll be red, tender, warm, and it will weep clear or ink-tinted plasma. Normal. Days four to fourteen: peeling and flaking, sometimes dramatic, often alarming, entirely expected. Weeks two to four: the peeled tattoo looks dull, cloudy or milky as a fresh layer of skin matures over the ink. Around six to eight weeks the surface is settled and the colours come back to true. Full deep healing of the dermis takes a few months.
Two panics account for most aftercare messages artists receive. First: 'my tattoo is coming off in the flakes.' It isn't; the ink sits in the dermis, below the layer that peels, and the tinted flakes are just dead surface skin. Second: 'it looked amazing and now it's dull and patchy.' That's the milky phase. Judge nothing before six weeks. If a genuine gap remains once fully healed, your artist will touch it up, and most include one within the first few months.