Why the Rule of 72 matters
The Rule of 72 isn't intrinsically important, but the concept of compound interest, or compound returns, is. Albert Einstein reputedly called it "the most powerful force in the universe." The Rule of 72 is simply a mental shortcut that helps investors easily understand and apply this powerful force.
To further underscore the importance of compound returns, consider Warren Buffett. When he was around 30 years old, he became a millionaire. And when he was 56 years old, he became a billionaire.
In other words, it took Buffett about 26 years to accrue 99% of his first $1 billion. But thanks to compounding returns, his net worth soared to around $44 billion over the subsequent 26 years. As of this writing, his net worth is $121 billion, according to Bloomberg, just 11 years after being worth $44 billion.
As author Morgan Housel writes in his book The Psychology of Money: "[Buffett's] skill is investing, but his secret is time. That's how compounding works."