A long-standing coaching convention that weekly running volume should rise by no more than about 10% from one week to the next. It is a rule of thumb rather than a physiological constant: it exists because most runners get injured by jumping volume quickly, not because 10% is a measured safe threshold. Treat it as a default that a conservative runner tightens and an experienced one occasionally exceeds.
Most marathon plans include them, and this calculator schedules one every third or fourth week depending on what you pick. A cutback week drops volume back so the body absorbs the previous block, then the build resumes from the last build week rather than from the reduced one. Skipping them entirely means every week is a new maximum, which is exactly the pattern that produces overuse injuries.
That depends on the gap between where you are and where you want to be. This tool gives the honest answer in weeks: at 10% a week with cutbacks, going from 30 to 60 kilometres a week takes noticeably longer than most runners assume, which is useful information when a goal race is already on the calendar.
The rule is usually applied to weekly totals, not to a single run. Jumping the long run sharply while keeping the weekly total flat still concentrates the stress in one session. A common approach is to hold long-run growth to a similar rate and to alternate a longer week with a steadier one.
Work backwards from race day. This calculator tells you how many weeks the ramp takes, and the training start date calculator counts back from any Major's real race date by a 12, 16, 18 or 20 week plan so you can see whether the ramp fits.