Rule of 72 is a quick way to estimate how long it takes an investment to double at a given growth rate. It sits in the Cognition dimension (COG) of the Human Behavior Taxonomy™ as element HBT-COG-0591, within the Probability family. The core principle: a quick way to estimate how long it takes an investment to double at a given growth rate. In incentive terms, it matters because it changes the payoff people perceive before they choose — which means it can be designed for, or exploited.
Scientific Definition
A quick way to estimate how long it takes an investment to double at a given growth rate.
Plain-English Definition
A quick way to estimate how long it takes an investment to double at a given growth rate.
Feynman Explanation
Math for people who need the answer before the meeting ends.
Core Principle
A quick way to estimate how long it takes an investment to double at a given growth rate.
Mechanisms
Pending editorial review.
A quick way to estimate how long it takes an investment to double at a given growth rate.
Pending editorial review.
Pending editorial review.
Pending editorial review.
Pending editorial review.
The rule of 72 makes compound growth intuitive.
Inputs (Triggers)
Pending editorial review.
Outputs (Behaviors)
Pending editorial review.
Behavioral Signature
Math for people who need the answer before the meeting ends.
Examples
- At 7% growth, money doubles in about 10 years.
- The rule of 72 makes compound growth intuitive.
Pending editorial review.
Original analysis from The Incentives Lab — how this element behaves inside real payoff structures.
Why this element matters to incentive design
The mistake with this element is treating it as irrationality. It is almost always a rational response to a payoff nobody wrote down. The mechanism underneath it is straightforward: a quick way to estimate how long it takes an investment to double at a given growth rate. You can recognize it in the field by its signature: math for people who need the answer before the meeting ends. Every element in the Cognition dimension changes the perceived payoff of an action before the action happens, which is exactly where incentive design has leverage.
How it gets exploited
Left undesigned, the rule of 72 makes compound growth intuitive. It is amplified whenever the rule of 72 makes compound growth intuitive. Inside organizations that shows up as the rule of 72 makes compound growth intuitive. The pattern is the same one Goodhart's Law describes: the measurable proxy attracts the effort, and the purpose behind it quietly loses funding.
How the Lab designs around it
The redesign move is to use it to sanity-check growth and interest projections. Watch for it at the boundaries: handoffs, promotions, incident reviews, and budget cycles are where this element gets its power.
Famous Experiments
Pending editorial review.
Design Principles
- Use it to sanity-check growth and interest projections.
Measurement Approaches
Pending editorial review.
Evidence
Pending editorial review.
Pending editorial review.
The Perverse Incentive Lens™
How this behavior is exploited — and how to redesign around it.
- Use it to sanity-check growth and interest projections.
Pending editorial review.
Pending editorial review.
Interactive Mini Network
Click any neighbor to re-center the graph and follow the threads of connection.
Knowledge Graph Neighbors
Auto-linked to the rest of the Human Behavior Taxonomy by family, domain, dimension, and shared keywords.
Posterior = (likelihood × prior) / evidence.
Ignoring general statistics in favor of specific, vivid information.
Update beliefs in proportion to the strength of new evidence.
Start with a prior; update with new evidence.
Novices experiencing early success, often due to variance and small samples.
High-impact, hard-to-predict, retrospectively explainable events.
Striking pattern that is statistically expected in large samples.
Reasoning in distributions — ranges and probabilities — rather than points.
Average outcomes across the population differ from outcomes across time for one person.
A rough calculation using order-of-magnitude reasoning.
In quantum mechanics, certain pairs of properties cannot both be precisely known.
We ignore sample size when judging probability.
Where Rule of 72 is cited in the corpus
Essays, field guides, and diagnostics from The Incentives Lab that apply this element.
- EssayGoodhart's Law in the Real World
How measurable proxies capture judgment.
- EssayThe Perverse Incentives Hiding in Your KPIs
Cognitive shortcuts turned into scorecards.
- EssayAI Agents Inherit Your Incentives
How this element propagates into automated systems.
- CourseIncentives 101
The free ten-part primer on reading a payoff structure.
- ReferenceThe incentive glossary
Definitions for every mental model, bias, and fallacy in the corpus.
- ReferenceThe Periodic Table of Human Behavior
The full 1,267-element map this page belongs to.
Questions about Rule of 72
- What is Rule of 72?
- Rule of 72 is a quick way to estimate how long it takes an investment to double at a given growth rate. It sits in the Cognition dimension (COG) of the Human Behavior Taxonomy™ as element HBT-COG-0591, within the Probability family. The core principle: a quick way to estimate how long it takes an investment to double at a given growth rate. In incentive terms, it matters because it changes the payoff people perceive before they choose — which means it can be designed for, or exploited.
- What is an example of Rule of 72?
- The rule of 72 makes compound growth intuitive. The Incentives Lab catalogs everyday, organizational, and historical instances of this element on its Human Behavior Taxonomy™ page (HBT-COG-0591).
- How is Rule of 72 exploited?
- The rule of 72 makes compound growth intuitive.
- How do you design around Rule of 72?
- Use it to sanity-check growth and interest projections.
- Which behavioral dimension does Rule of 72 belong to?
- Rule of 72 is classified in the Cognition dimension (COG) of the Human Behavior Taxonomy™, family "Probability", class "Mental Model". Its permanent identifier is HBT-COG-0591 and its evidence grade is B.