Getting Started
Interview Structure
The four phases of a 45-minute interview, and how to manage your own clock.
A 45-minute system design interview has a shape, even when the interviewer doesn't announce it. Knowing the shape ahead of time means you spend your time on the work instead of guessing what phase you're in.
The four phases
The exact minutes vary by interviewer, but this split is a widely-used rule of thumb for a 45-minute loop, and a reasonable default to rehearse against if you don't know the company's format in advance:
Requirements
0–8 min
High-level design
8–23 min
Deep dive
23–43 min
Wrap-up
remaining time
| Phase | Typical share of the time | What you're doing |
|---|---|---|
| Requirements | 5–8 minutes | Scoping the problem, naming constraints, agreeing what "done" means |
| High-level design | 10–15 minutes | A first architecture that satisfies the requirements, at a coarse grain |
| Deep dive | 15–20 minutes | The interviewer picks one or two components and pushes on them |
| Wrap-up | remaining time | Trade-offs, failure modes, what you'd do with more time |
This is the phase breakdown Time Management gets scored against: not "did you finish," but "did you spend your minutes where the signal actually is."
Watch for phase transitions
Interviewers rarely say "let's move to the deep dive." The signal is usually a narrowing question — "walk me through what happens when two writes race" or "how does this behave when that service is down." Treat a narrowing question as permission to stop expanding the design and start defending one piece of it.
Managing your own clock
Say the time budget out loud early: "I'll spend a few minutes on requirements, then sketch the high level, and leave time for you to dig into whatever matters most." This does two things — it shows you understand the format, and it gives you a reason to redirect if the requirements discussion runs long.
If you finish the high-level design with time to spare
Don't pad it with more boxes. Name the two or three places you'd expect the interviewer to push, and start narrating trade-offs there yourself. It signals the same seniority a good deep dive would, without waiting to be asked.