The Rule of 72

This is a handy little way to estimate doubling time based on yearly percentage growth.

For example:

If the world-wide population is growing at 1.5% a year, 72 divided by 1.5 is 48 years. Right now we have 7 billion on the planet. Do you think this planet can handle 14 billion people? In just 48 years?

If inflation is 4% a year, 72 divided by 4 is 18 years.  Your dollar will buy half of what it does now in 18 years.  Makes saving for retirement twice as hard now doesn’t it?

If crude oil production falls by 2% a year, 72 divided by 2 is 36 years. What’s the world going to look like with half as much cheap energy around?

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