The first 90 days at a new developer job determine your trajectory for the next 2-3 years. No pressure. I have seen developers get promoted within six months of starting. I have also seen talented engineers get fired during their probation period — not because they could not code, but because they misread the room. The difference between these outcomes almost never comes down to technical skill. It comes down to how you navigate the first 90 days. This is the guide I wish someone had handed me on day zero. Not generic career advice. Specific, tactical moves for software developers entering a new team. The 90-day window is not arbitrary. Research from the Society for Human Resource Management shows that 90 days is roughly the time it takes for a new hire to either integrate into the team or start showing signs of misfit. It is also the standard probation period at most companies — which means someone is actively evaluating you during this time. Here is what your manager is actually looking for during each phase: Days 1-30: Can this person learn? Are they asking the right questions? Do they fit the team culture? Days 31-60: Can they contribute? Are they picking up tasks independently? Do they communicate clearly? Days 61-90: Can they own things? Are they reliable? Would I trust them with a critical feature? Notice that "Can they write brilliant code?" does not appear on this list. That is because your manager already assumes you can code — they hired you. What they are evaluating now is everything else. Most developers treat the period between accepting the offer and starting the job as vacation time. Smart developers treat it as preparation time. Do not just skim the company's "About" page. Go deep: Download and use the product. If it is a web app, sign up. If it is a mobile app, install it. Use it for a week. Note bugs, confusing UX, things you like. This gives you context that no onboarding document can provide. Read the engineering blog. Most tech companies have o