> ## Documentation Index > Fetch the complete documentation index at: https://www.planmyrounds.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # How seniority and senior/junior mix work > Every doctor is Senior or Junior, and shifts can require a minimum number of seniors — here's how that level is used across scheduling. Every doctor profile has a **Level**: Senior or Junior. It's a single field, but it feeds several parts of scheduling. ## Where seniority is used A shift's [Min Seniors Required](/docs/concepts/coverage-requirements) sets how many of its required doctors must be Senior. This is a hard constraint. On organisations using the advanced scheduling engine, shifts can require a defined ratio — for example, one senior for every three juniors. Also a hard constraint. See [Roster constraints](/docs/rosters/roster-constraints#senior-to-junior-ratio). The engine's first solving pass assigns senior doctors before filling remaining slots — see [Solver behaviour](/docs/scheduling-engine#solver-behaviour). Senior doctors are marked with an asterisk (`*`) next to their name, so you can confirm the ratio on any given day at a glance. ## If a shift can't meet its senior requirement If there aren't enough active, eligible senior doctors to satisfy every shift's Min Seniors Required or ratio across the period, generation fails — this is one of the more common failure causes on smaller teams. See [Duty Plan generation failed](/docs/troubleshooting/duty-plan-generation-failed). ## Next steps Set or correct a doctor's Level. How Required Doctors and Min Seniors Required work together.