TLDR
- Fat FIRE means reaching financial independence on a generous budget, often described as around $100,000 a year or more in spending.
- At a 4% withdrawal rate, $100,000 a year needs about $2.5 million invested. At 3.5%, about $2.86 million.
- Saving $3,000 a month at 5% a year after inflation, $2.5 million takes about 30 years. Saving $8,300 a month takes about 16.
- Saving $8,000 or more a month after tax and after a comfortable lifestyle needs a large income. It usually comes from one of three places: an inheritance, a high salary, or a business with many clients.
Fat FIRE is the version of financial independence where you don’t cut back. You keep the home, the holidays and the school fees, and your investments pay for all of it.
The arithmetic is simple. The income it needs is the hard part, and most writing about Fat FIRE skips straight past it.
The Fat FIRE number
Your number is what you spend in a year, divided by the withdrawal rate you trust. Most people aiming for Fat FIRE use a more cautious rate, because a bigger pot has further to fall in a bad decade.
| Yearly spending | At 4% | At 3.5% | At 3% |
|---|---|---|---|
| $100,000 | $2.5 million | About $2.86 million | About $3.33 million |
| $150,000 | $3.75 million | About $4.29 million | $5 million |
How long it takes
Here’s $2.5 million, starting from zero, at 5% a year after inflation:
| Saved per month | Years to $2.5 million |
|---|---|
| $3,000 | About 30 |
| $5,000 | About 23 |
| $8,300 | About 16 |
| $8,300, with $350,000 already invested | About 13 |
Look at the third row. Saving $8,300 a month is $100,000 a year, after tax, while also living the $100,000 lifestyle you’re saving for. That’s a household bringing home something like $200,000 a year, every year, for sixteen years.
Fat FIRE isn’t a saving problem. It’s an income problem.
Where that income usually comes from
There are really three ways to that income. You inherit it. You earn a very high salary. Or you build and own a profitable business.
Inheriting isn’t a plan. A high salary works for some, such as senior doctors, lawyers, and people in finance and tech, but it’s one income from one employer. One restructuring and it’s gone. A single income that size is the scary version, however good it looks.
A business with many clients is different. No single client can switch the income off, and it can grow past what a salary offers. A service business that pays its owner $200,000 a year is not unusual. And a business does something a salary never does: it can be sold. The fourth row is what happens when part of the pot arrives as a lump, from a sale or anything else, instead of being saved a month at a time.
My first salary was $1,700 a month. No amount of saving from that was going to reach Fat FIRE. What changed the maths was selling the same skill directly, and later building a business that could run without me.
The catch with using a business
A business only helps your Fat FIRE number in two ways: what it pays you while it runs without you, and what lands if you sell it. A business that needs you every day is a high-paying job. Count what you save from it, nothing more.
And a sale lands less than its headline price, after the earn-out, fees and tax. Here’s how to work out the price you’d actually need, and how much your business really counts toward your number.
Run your own
Open the calculator. If you’re building toward it, pick “I don’t have a business yet” and see what a second income does to your date. If you already own one, pick “I already own one” and compare walking away with sticking it out. The six levels of a service business shows where the income usually comes from at each step.
Illustrative numbers, not advice. I’m not a licensed adviser; I show the maths and what I did, and you run yours.