Generally speaking and in most cases budgies will start their first moults after reaching 3 months old (12 weeks of age). Some can start as soon as they reach that age mark, while others can start a bit later at about 4 months old.
This is where they will usually lose the barring on the forehead area and replace some of their throat spots (and also cheek patches) as well as some normal body feathers on chest/tummy.
At about 6 - 7 months old, they go through a second moult where they will usually replace some tail feathers and flight feathers (and body feathers).
After fully completing the first two moults, budgies will then go through two major moults per year, usually during Spring and at Fall.
This doesn't mean that they will not have other minor moults throughout the year, as these can be triggered by some factors such as stress, change of diet, etc.
As for the visual changes that budgies go through when moulting, depending on colour mutations, some changes can be more drastic, especially if a budgie is yellow face or golden face. Apart from that and in general after the first moult is completed, the body feathers will have richer and more vibrant colour.
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