Estimate time to learn a skill.
Time to skill depends on effective practice hours rather than elapsed hours, which is why the efficiency factor matters. Repeating what you can already do accumulates hours without building capability; deliberate practice at the edge of your ability is what counts. Discounting weekly hours by the deliberate share gives a realistic timeline — five hours a week at 70 percent deliberate is three and a half effective hours.
Time to proficiency from effective practice
Effective weekly = practice hours x deliberate share; hours remaining = target - logged; weeks = remaining / effective weekly
Around 20 hours for basic competence at something simple, 100-300 for working professional proficiency in a defined technical skill, and thousands for genuine expertise. The often-quoted 10,000 hours refers to elite performance, not usefulness.
Working on something you cannot yet do, with immediate feedback and correction. Watching tutorials, re-reading notes and repeating exercises you have already mastered all accumulate hours without much learning.
Up to a point. Consolidation happens between sessions, so five focused hours across five days beats five hours in one sitting. Beyond about fifteen or twenty hours a week the deliberate share tends to fall as fatigue rises.