Stock and Flow
Updated 2026-07-31
INTRODUCTION
English translation pending.
CORE DEFINITION
Stock and flow is the foundational structure of system dynamics. A stock is an accumulation measured at a moment, such as water in a bathtub or money in an account. A flow is a rate that changes a stock over time, such as inflow and outflow. Confusing the two leads to misreading situations, because a high stock can hide a negative net flow, and the resulting change becomes visible only after a delay.
SCAFFOLDING EFFECT
Reduce cognitive load
- Structure split: separate the accumulated quantity from the rates that change it. - Lag awareness: see how a healthy stock can conceal a negative flow until it is depleted. - Lever choice: manage the stock by adjusting flows and setting safety thresholds.
Anchor fast decisions
Stocks change only through flows, so the state visible today reflects past flows and conceals current ones. When inflow falls below outflow, the stock keeps declining quietly until the deficit becomes apparent. Because of this lag, decisions based on the stock snapshot alone arrive systematically late.
MINIMUM ACTION
In progress 0/4Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Stock_and_flowverified
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