Compound Interest
Compound interest is the process where interest earned is added to the principal, generating further interest and leading to exponential growth over time. It applies to finance as well as relationships, habits, learning, and fitness.
THE IDEA
Compound Interest
Overview
Compound interest is the eighth wonder of the world. He who understands it, earns it, he who doesn’t, pays it. —Albert Einstein
Compound interest appears when the interest generated is added to the initial capital, which causes the interest generated at first to generate new interest again.
Compound interest has a multiplier effect on investments, since new interest is generated from previously accumulated interest and then added up to it. This makes compound interest a great ally for long-term investment.
Formula and Calculation
The formula for calculating compound interest is:
Compound Interest = Total amount of Principal and Interest in future (or Future Value) minus Principal amount at present (or Present Value)
= [P (1 + i)<sup>n</sup>] – P
= P [(1 + i)<sup>n</sup> – 1]
Where: P = Principal, i = nominal annual interest rate in percentage terms, and n = number of compounding periods.
Example
Take a three-year loan of $10,000 at an interest rate of 5% that compounds annually. What would be the amount of interest? In this case, it would be:
$10,000 [(1 + 0.05)<sup>3</sup> – 1] = $10,000 [1.157625 – 1] = $1,576.25.
Beyond Finance
All the benefits in life come from compound interest—money, relationships, habits—anything of importance. —Naval Ravikant
With compound interest, the below aspects of life can offer other good examples:
- Relationships
- Fitness / Sports
- Learning / Knowledge
- Habits
When to use it
Long-term retirement investing where early contributions have decades to compound.
Building a daily exercise routine that gradually improves fitness and prevents decline.
Learning a new language through short daily practice sessions that accumulate vocabulary.
Strengthening relationships with regular, small acts of kindness that build trust over time.
FROM THEORY TO EVERYDAY LIFE
In practice
Financial Investment
Investing $10,000 at 5% annual compound interest grows to $11,576.25 after 3 years, compared to only $11,500 with simple interest, demonstrating the multiplier effect of earning interest on interest.
Habit Formation
Reading 20 pages of a book each day compounds into over 30 books a year, dramatically expanding knowledge over time through consistent small efforts. The accumulated knowledge builds upon itself, making learning more efficient.
A MOMENT TO REFLECT
Put it to work.
How can you apply the principle of compound interest to your daily habits?
In what areas of your life are you seeing the compounding effects of small consistent actions?
How might the compounding of knowledge change your approach to learning new skills?
Often confused with
CONTINUE THE CONVERSATION
Source texts
- Wisdom Theory 100 Mental Models (2020) (Wisdom Theory)