How much ownership should a sole software developer get in a software startup?

A sole software developer in a startup typically should consider owning between 20% to 50% of the company, depending on their contributions, the value of the idea, and the involvement of other co-founders or investors. If the developer is the sole founder and driving the project, a higher percentage is justified. However, if they are joining an existing team, their equity might be lower, reflecting their role and the resources invested by others. Ultimately, equity should align with the developer's contributions and the company's growth potential.