How Coast FIRE works
Coast FIRE is the point where you have enough invested that you can stop saving entirely and still reach full financial independence by your target retirement age. Growth alone gets you there. To find the number, start with your full FIRE number: your annual spending times 25, which is the flip side of the 4% withdrawal rule. Then discount that target back to today using your expected real return over the years you have left. The result is your Coast FIRE number. If what you have invested already beats it, you have coasted.
Coast FIRE vs FIRE, Lean FIRE, Barista FIRE and Fat FIRE
Regular FIRE means the full pot is in place and work becomes optional today. Coast FIRE is earlier and lighter: you still work to cover living costs, but not a cent has to go toward investing, because the portfolio is on track by itself. Barista FIRE sits in between, where part-time work, often taken for health cover, tops up the gap while investments coast. Lean FIREand Fat FIRE describe the size of the target rather than the timing: Lean FIRE aims at a frugal budget, so a smaller FIRE number, while Fat FIRE aims at a comfortable, no-compromise lifestyle and a much larger one. Coast FIRE tends to be the first milestone people reach, and the one that changes how work feels, because the pressure to save is off.
Why the real-return assumption matters
The single biggest lever in this calculation is the real return, the growth rate after inflation. Because it is after inflation, your spending stays in today's money and the maths holds together. Historically a stock-heavy portfolio has returned somewhere around 5% to 7% real over the long run, but nothing is guaranteed. A more cautious assumption raises your Coast FIRE number, since you are betting on slower growth. For founders and solopreneurs, hitting Coast FIRE is about buying back optionality: the freedom to take the lower-paid, higher-upside bet because retirement is already handled.
Frequently asked questions
How do I calculate my Coast FIRE number?
Two steps. First work out your full FIRE number: your annual retirement spending times 25 (the 4% rule). Then discount it back to today by dividing by (1 + your real return) raised to the number of years until you retire. If you have $50,000 of spending and retire in 30 years at a 7% real return, your FIRE number is $1.25M and your Coast FIRE number is about $164,000.
What is a good Coast FIRE number?
There is no single good number. It is personal, driven by your target spending, your age, and how many years of compounding you have left. The younger you are, the smaller your Coast FIRE number, because your money has longer to grow. Someone 30 years from retirement might need under $170,000, while someone 10 years out needs far more for the same lifestyle.
How much do I need for Coast FIRE?
Enough that compound growth alone carries it to your full FIRE number by retirement, with no further contributions. Enter your spending, age, and expected real return above and the calculator returns the exact figure. As a rough guide, the further you are from retirement, the less you need invested today.
What is the difference between Coast FIRE, regular FIRE and Barista FIRE?
Regular FIRE means you have the full portfolio to live off investment returns and stop working entirely. Coast FIRE means you have enough invested that you can stop saving, cover only your living costs from work, and still hit full FIRE by retirement. Barista FIRE sits between the two: you work part-time, often for benefits, to top up while investments coast.
Why does the real return assumption matter so much?
Because it is what discounts your future FIRE number back to today. A real return is the return after inflation, so keeping your spending in today's money stays consistent. Shift the assumption from 7% to 5% and your Coast FIRE number rises sharply, since you are assuming slower growth. Use a figure you would be comfortable relying on for decades.
Does Coast FIRE assume I stop contributing?
Yes. That is the whole idea. Once you reach your Coast FIRE number you can stop adding new money and let compounding finish the job. You still need income to cover your living costs until retirement, but none of it has to go toward investing. That is the optionality Coast FIRE buys you.
How do I calculate my FIRE number?
Your FIRE number is the portfolio that funds your retirement from investment returns alone. The quick method is your annual retirement spending times 25, which is the 4% withdrawal rule in reverse. On $50,000 a year that is a $1.25M FIRE number. Lower your spending or your withdrawal rate and the number falls. This calculator works out that full FIRE number, then discounts it to today to give your Coast FIRE number.
What are Lean FIRE and Fat FIRE?
They describe the size of your target. Lean FIRE aims at a frugal budget, so a smaller FIRE number that is quicker to reach but leaves less room. Fat FIRE aims at a comfortable, no-compromise lifestyle and a much larger number. Both use the same times-25 maths, just with different spending. Set your own target spending above and the calculator shows the FIRE and Coast FIRE numbers for it.
This tool is a guide, not financial advice.
