The Rule of 72: Understand and Learn how to Calculate

A lesson for students about Rule of 72 and its use in determining when your money or investment will double. Explore compound interest and the effects of different interest rates.

Students learn the fundamental principle of the “Rule of 72” and compound interest. This lesson dives into understanding how the Rule of 72 aids in estimating the number of years required to double your money with a fixed annual rate of return. Beyond just the rule, you will be introduced to the significance of compound interest and how different rates can greatly influence the growth of your investment over time, emphasizing the importance of starting early.


Use this video lesson on the topic of the Rule of 72 basics. Learn related concepts of:

  • Investment Basics
  • Career Planning
  • Compound Interest
  • Earning Income
  • Saving
  • Investing
  • Financial Planning


9-12th grades. High School. College. Adult Education.


45-60 minutes. Adjust the lesson plan and allocate time to certain topics based on the needs and interests of the students.


Hand out the worksheet below (see the GET LESSON button near the bottom of the page).

Show students the video and have them complete the worksheet.  Review the questions on the worksheet.  A more comprehensive and detailed lesson plan can be accessed below for further instruction and study.

The Rule of 72 | Understand and Calculate

After watching the video, have students tell what the most important things they learned from the video.


Lesson Plan: The Rule of 72 | Understand and Calculate



By the end of the lesson, students will be able to understand and apply the Rule of 72 to calculate the time needed for an investment to double at a fixed interest rate.


  • Video titled “The Rule of 72 | Understand and Calculate”
  • Calculator
  • Whiteboard or projector for displaying tables and formulae


  1. Introduction (10 minutes):

    • Begin by asking students if they know how long it would take for their money to double if they were given a certain interest rate.
    • Introduce the video titled “The Rule of 72 | Understand and Calculate.”
  2. Video Viewing (15 minutes):

    • Play the video for the students.
    • Pause occasionally for clarifications if needed.
  3. Discussion Questions (15 minutes):

    • Why is the Rule of 72 important for financial planning?
    • How does the Rule of 72 relate to compound interest?
    • Why is the number 72 used in this rule?
    • How does a higher interest rate affect the time it takes for money to double?
  4. Activity: Calculation Practice (15 minutes):

    • Give students a set of interest rates.
    • Ask them to use the Rule of 72 to calculate how long it will take for investments to double at those rates.
    • Discuss their answers as a class.
  5. MI Chat chatbot Activity (20 minutes):

    • Introduce students to the “MI Chat chatbot”.
    • Explain that the chatbot will ask them questions about the Rule of 72.
    • Allow students to interact with the chatbot, answering its questions and seeking clarifications if needed.
    • After the session, discuss the chatbot’s questions and the students’ answers to ensure understanding.
  6. Quiz (10 minutes):

    • Distribute a short quiz to assess students’ understanding of the Rule of 72.
    • The quiz includes questions about the formula, its application, and its significance.
  7. Conclusion (5 minutes):

    • Recap the importance of the Rule of 72 in financial planning and the magic of compound interest.
    • Remind students about the benefits of early and consistent investing.


Ask students to research real-life examples of investments and use the Rule of 72 to calculate the doubling time. They can present their findings in the next class.


Students’ participation in the discussion, their performance in the activity and chatbot interaction, and their scores on the quiz will determine their understanding of the topic.


  • Dive deeper into the world of logarithms to explore the mathematical basis for the Rule of 72.
  • Explore other financial rules and formulas that are useful for personal finance planning.

Lesson Resources

MI Chat Chatbot Tool

  • The rule of 72 questions with MI Chat chatbot – Use the MI Chat chatbot to test your students’ understanding of the lesson. The MI Chat chatbot is an interactive platform designed to deepen understanding, aligning with specific queries and thoughts. Offering personalized insights, it directs users toward a clearer grasp of topics, ensuring they match their learning pace, knowledge level, and cognitive goals.

Get Lesson


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