What is Coast FIRE
Coast FIRE is a milestone rather than a destination. Reaching it does not mean you can stop working — it means you can stop saving for retirement specifically, because what is already invested will get there on its own given enough time.
The arithmetic is a single compound-growth calculation run backwards. If you need $1.5 million at 65, expect a 5% real return, and you are 35, then you need roughly $347,000 invested today for compounding alone to close the gap. Anything you earn after that only has to cover the years between now and then.
Its practical value is psychological and it is considerable. Hitting Coast FIRE converts retirement saving from an open-ended obligation into a solved problem, which is what makes a lower-paid job, a sabbatical or a career change financially survivable rather than reckless. The result is extremely sensitive to the real return you assume — the difference between 5% and 7% over thirty years is close to a factor of two. The Coast FIRE-by-age table is the same identity for every age from 25 to 60. If you want to drop to part-time now instead of later, the Barista FIRE calculator sizes that gap.
The calculator
You are $197,066 short of Coast FIRE. At 5.0% real over 30 years, you would need $347,066 invested today for compounding alone to reach $1,500,000.
How it works
Spending divided by the withdrawal rate is the retirement target (4% = 25×). That target is discounted back to today at the real return. With the figures above, $1,500,000 over 30 years at 5.0% is $347,066 today.
Assumptions
One constant real return, no fees, and a withdrawal rate that holds for your horizon. Markets do not deliver a constant return — see the sequence of returns calculator. A 1% fee is a large change over decades; the fee calculator sizes it.