You have probably heard of FIRE (Financial Independence, Retire Early) — but have you heard of Coast FIRE? It is an earlier, lighter stage of the FIRE movement: you save enough money now that it grows on its own to your retirement target, then you never have to add more. Today we explain Coast FIRE: how to calculate it, how it differs from standard FIRE, and who it suits.
What Is Coast FIRE: Hand the Principal to Compound Interest and Coast
The core idea in one sentence: save enough today that it compounds into your retirement target by retirement age, then your working income only needs to cover daily expenses — no further retirement saving required. Your saving "mission" ends the day you hit Coast; time and compounding do the rest.
Example: Xiao Liu is 30 and wants 3 million yuan by retirement at 60. At a 6% annual return, work backward with compounding: 3,000,000 ÷ (1.06)^30 ≈ 3,000,000 ÷ 5.74 ≈ 520,000. In other words, at 30 he only needs to save about 520,000 yuan — then he never has to save for retirement again. That money will compound to 3 million by 60. That is his "Coast number."
Use our compound interest calculator to compute your own Coast number precisely: enter the target amount, the years from now to retirement, and the expected annual return, and reverse-engineer what you need to save today. Then use the retirement calculator to sanity-check the target — the Coast number is "target ÷ compound factor," so it is only as good as the target.
| Current Age | Retirement Target | Coast Number at 6% | Coast Number at 8% |
|---|---|---|---|
| 25 (35 years to retirement) | 3 million | about 390k | about 200k |
| 30 (30 years) | 3 million | about 520k | about 300k |
| 35 (25 years) | 3 million | about 700k | about 440k |
| 40 (20 years) | 3 million | about 940k | about 640k |
The table is telling: the earlier you hit Coast, the less principal you need. At 25, 390k achieves Coast; at 40, 940k — 15 years later, the requirement more than doubles. That is "compound interest is time's friend" in its most vivid form.
Coast FIRE vs Standard FIRE: Different Stages, Different Goals
FIRE has several stages, and Coast FIRE is the earliest stop:
Standard FIRE (Lean/Fat FIRE): the goal is to save, during your working life, a principal that covers all post-retirement living costs, then fully retire and live on investment returns. Under the 4% rule, spending 120,000 a year needs 3 million; save 3 million and you can retire completely.
Coast FIRE: the goal is not 3 million now, but the present value that will become 3 million by retirement — say 520,000. After hitting Coast you keep working (for living costs and your current life), but your retirement savings are "automatically done." Coast FIRE's core value is removing the pressure of "must save for retirement" while you are still young.
Use our CAGR calculator to align the two: standard FIRE asks "does current principal × 4% cover my annual spending?"; Coast FIRE asks "does current principal × compounding reach my retirement target?" The former answers "can I retire now," the latter "can my retirement savings grow on their own."
| Comparison | Standard FIRE | Coast FIRE |
|---|---|---|
| Goal | Save all post-retirement costs | Save the present value that will be enough |
| Working after? | Fully retired | Keeps working, no more retirement saving |
| Principal needed | High (e.g. 3 million) | Low (e.g. 520k) |
| Key asset | Current investable principal | Time × compound interest |
| Best for | Those who want to retire early | Those who want less saving pressure but still work |
Coast FIRE is an attractive intermediate target: for most people, sprinting straight to standard FIRE is too distant and easy to abandon, but reaching Coast FIRE is feasible — it turns "financial freedom" from a faraway dream into an executable milestone.
Three Risks of Coast FIRE and Who It Suits
Coast FIRE sounds great, but three risks must be recognized:
Risk one: the return assumption may fall short. The Coast number depends on a long-term annual return assumption (6%-8%). If actual returns come in below expectations, the principal may not reach the target in 30 years. To be safe, use a conservative rate (5%) or run a stress test across a rate range.
Risk two: inflation and growing expenses. The Coast number is in today's purchasing power, but retirement costs rise with inflation. If the target ignores inflation or future cost increases (health care, elder care), you will actually need more. Adjust the target upward for inflation each year.
Risk three: life changes before retirement. Job loss, illness, or a surge in family expenses can force you to dip into that "untouchable" Coast principal. Coast FIRE presupposes the money can sit untouched for decades — which is not always realistic.
Coast FIRE suits people who: earn reasonably, can save, but do not want to sacrifice today's quality of life for retirement; trust compounding and will hold long-term without tinkering; and want a reachable milestone for retirement savings. It does not suit those with aggressive return assumptions or large upcoming expenses (home purchase, children's education) — for them, calculate the Coast number conservatively.
Implementation: first compute your Coast number with the compound-interest calculator, then stress-test it across return rates with the CAGR calculator, and finally set the target at the "conservative" end — better to save a little more than to gamble on compounding. After hitting Coast, put the principal in a long-term, stable portfolio and let time complete your retirement savings while you focus on work and life.
FAQ
Q1: After Coast FIRE, do I really never save again?
You stop saving "for retirement," but you still work to earn for your current life. After Coast, working income only needs to cover daily expenses; retirement savings are completed by principal and compounding. The precondition is that the principal grows at the assumed rate and you never touch it.
Q2: Is Coast FIRE the same as Barista FIRE?
No. Barista FIRE is an early-retirement form where you take a light part-time job (like a barista) after retiring to subsidize living costs — the emphasis is on continued income after retirement. Coast FIRE's emphasis is that the saving phase is over and principal grows via compounding; it does not emphasize the type of work after retirement.
Q3: What return rate should I use for the Coast number?
Use a conservative 5%-6%. High rates (8%+) produce an attractive Coast number but leave little margin for error. With 5%, you save a bit more; outperformance is a pleasant surprise, and underperformance will not collapse the target.
Q4: Where should the Coast principal be held after reaching it?
In a long-term, diversified, stable portfolio: index funds, bonds, conservative wealth products. The key is "hold long-term, do not trade frequently" — the Coast principal relies on compounding and time, and frequent trading only erodes returns. Lower risk tolerance can lean toward bonds, but long-term returns drop accordingly.
Q5: I am 45. Is Coast FIRE still possible?
Yes, but the principal requirement is higher. The closer to retirement, the shorter the compounding period and the larger the Coast number (at 45, 20 years to 3 million at 6% needs about 940k). Near retirement, Coast FIRE's advantage fades — it is more appropriate to evaluate standard FIRE directly or save as needed.