My mother was an eighth-grade math teacher, so you can imagine her reaction when I was asked not to return to the advanced placement math class in junior high due to my lack of comprehension of the subject.   I never did quite "get" math class, which naturally caused me to find a field where math is not a prerequisite...law.  

Thankfully, the math behind FIRE (Financial Independence Retire Early) is straight forward: Figure out what you need to live each year, multiply by 25, and you now know your number.  Based on the widely accepted principles of the 4% safe withdrawal rate ("SWR"), which we will discuss and debate in a later post, once you reach your number, you can stop working and live off of those investments for the rest of your life.*

By way of example, if you were to spend $80,000 per year to survive (all expenses, on average), you would need to have $2MM socked away.  If you currently have $0 saved, and are putting away $1,000 per month, it would take you 37 years (assuming an average 7% annual return) to reach $2MM.  If you are starting your working life today (at 23 years old), you will be 60 by the time you save enough to retire.  I don't know about you, but retiring at 60 is not retiring early (key principle to the RE part of FIRE).  

Accordingly, you will need to shorten the amount of time it takes you to reach your number.  Short of winning the lottery, this can be done by pushing on one of two levers at your disposal: (i) reducing annual spending; or (ii) increasing annual savings, or both.

If you decrease your annual spending, to say $60,000 per year, your new number becomes $1.5MM ($60,000 x 25).  With the same rate of saving ($1,000 per month), you will reach $1.5MM during the 33rd year (at age 56).  But, if you also take the reduction in annual spending and save the difference (an added $1,666/month), you will reach your $1.5MM goal during the 21st year (at age 44).

This highlights the power of making wise financial choices early in life and how being intentional with spending can lead to greater financial flexibility in life.

My personal journey is well underway, but i wish I had given more thought to this principle a decade ago, I could have been halfway towards FIRE if I had.   

* There are a handful of times when the SWR would not have provided safe withdrawal for the rest of your life.  This article from Forbes gets into those details: https://www.forbes.com/sites/wadepfau/2016/04/19/the-4-rule-and-the-search-for-a-safe-withdrawal-rate/#583811775a10