Classic Retention
IntermediateClassic retention is the share of a cohort that was active on exactly day N after their first use, measured separately for each day.
This is the strictest definition of return, because activity on neighbouring days does not count, and the resulting curve drops steeply before flattening. For a product with a weekly rhythm it is misleading: such a product reads near zero on day three while being healthy, and the bumps on days seven and fourteen reflect a weekly habit rather than improvement. A classic retention figure is therefore only comparable with another classic retention figure, never with a more permissive definition.
How it is calculated
Classic retention on day N = cohort users active on day N ÷ cohort size
The denominator is always the original cohort size, not the survivors of the previous day, so the curve can move up as well as down. Day zero is the acquisition day and is normally excluded from the curve. The unit is a percentage.