Two different questions
FIRE (Financial Independence, Retire Early) asks: "Do I have enough invested, right now, to sustainably cover my living expenses indefinitely — so I could stop earning today?" It is a large number, usually quoted as your annual expenses divided by a chosen withdrawal rate (see our FIRE calculator).
That familiar shortcut carries an assumption worth naming: that your spending stays flat, in today's money, for the whole of retirement. Real retiree spending tends to run high through the active early years, ease through the seventies, then lift again later as care costs arrive — the spending smile. Modelling that shape generally produces a somewhat smaller number than the flat version, and our calculators show both so the difference is visible rather than assumed.
Coast FI asks a narrower, earlier question: "Is the retirement portion of my plan already on track through growth alone, assuming I keep working (and covering today's expenses some other way) until my planned retirement age?" It is typically a much smaller number, because it has decades of compounding left to do the work, rather than needing to be sufficient starting today.
Side by side
- What it answers — FIRE: "could I stop earning today?" Coast FI: "is my retirement growth on track if I keep working until retirement age?"
- Typical size of the number — FIRE: your full annual-expenses-based target, needed now. Coast FI: a smaller amount today, because it has years left to compound before it needs to cover anything.
- What changes once you get there — FIRE: you could plausibly stop working entirely. Coast FI: you can stop contributing specifically toward retirement, but you are still expected to earn enough to cover current living costs until retirement age.
- Timeline — FIRE is usually the end goal. Coast FI is typically reached years, sometimes decades, earlier — for the same person, on the same numbers.
Coast FI is an earlier, softer milestone — not a substitute
It is worth being precise about this, because the two are easy to conflate: reaching Coast FI does not mean you have reached FIRE, and it is not a shortcut to the same outcome. It is a different, smaller commitment. Someone who is Coast FI still needs an income to live on until they actually retire — that income just no longer needs to include ongoing retirement contributions for the math to keep working.
For some people, that flexibility is the whole point: it can open the door to a lower-stress job, fewer hours, or work that pays less but matters more — without derailing the retirement plan. For others, Coast FI is simply a waypoint they pass through on the way to full FIRE, with no change in behavior at all.
No advocacy either way
This is not a case for choosing one over the other. Full FIRE requires a much larger number and, for most people, many more years of aggressive saving — but it removes the need to earn at all. Coast FI requires far less and can be reached much sooner — but it still depends on continuing to earn a living until retirement age, and it carries the same assumption risk (returns, inflation, spending, and timeline can all turn out differently than planned) as any long-range projection.
Which milestone — if either — is worth targeting is a personal decision based on your own priorities, career, and risk tolerance. Run your own numbers with the Coast FI calculator and the FIRE calculator to see both pictures side by side, and read what Coast FI means in more depth.
Disclaimer
This guide is for informational and educational purposes only and is not financial advice, a recommendation, or a substitute for professional guidance. Individual circumstances, returns, and inflation vary. Consult a qualified financial professional before making decisions about your retirement plan.
How OptiAI helps
OptiAI keeps whichever number you're tracking — Coast FI, FIRE, or both — connected to your real net worth and goals, so you can ask an AI assistant how you are tracking instead of recalculating by hand.