Coast FIRE Explained
The version of early retirement most people miss
Coast FIRE is the portfolio size that, without any additional contributions, grows to cover your retirement expenses by traditional retirement age. Someone at Coast FIRE could theoretically stop saving entirely and still retire on schedule. They still work — but their paycheck covers current expenses, not retirement savings. It is often the earliest meaningful FIRE milestone, reachable 15–25 years before Full FIRE for most people. Understanding it changes how you think about the rest of your career.
The math, with real numbers
Someone wanting $60,000/year in retirement needs $1.5M at retirement (4% rule). If they retire at 65 and invest at 7% real returns, their Coast FIRE number by current age:
Coast FIRE at 25: $100,186. At 35: $197,077. At 45: $387,517. At 55: $762,524.
The pattern: the Coast FIRE number roughly doubles every decade closer to retirement. Someone starting 10 years earlier needs half the capital. This is why earlier matters so much in FIRE — not because “start early” is a platitude, because the math demands it. The Coast FIRE calculator computes your specific number for any combination of inputs.
What Coast FIRE actually changes about your life
Reaching Coast FIRE does not mean you stop working. It means you stop working for future retirement. Your current paycheck covers current expenses. Your future self is already funded.
Practical implications: you can reduce your savings rate dramatically (sometimes to zero). You can take a lower-paying job you actually enjoy. You can start a business that does not immediately pay well. You can take sabbaticals without derailing retirement plans. You can redirect income toward things like paying off a mortgage, children’s education, or simply living better now.
Coast FIRE is optionality. You might choose to continue saving aggressively — every additional dollar moves Full FIRE closer. But you are no longer required to.
The return assumption problem
Coast FIRE math depends entirely on your assumed return rate. At 7% real returns, reaching $200,000 at age 35 comfortably funds a $1.5M retirement. At 5% real returns, $200,000 becomes only $870,000 at 65 — far short of target.
Historical S&P 500 real returns have averaged about 7% long-term. But specific decade-long periods have produced 2–3% real returns. If you hit “Coast FIRE” assuming 7% and markets deliver 4% for the next 30 years, you are not at Coast FIRE at all. Conservative planning uses 5% real returns — that requires 40% more capital but provides meaningful protection.
Coast FIRE vs other FIRE variants
Lean FIRE: very low expenses (under $40K/year), $500K–$1M portfolio. Regular FIRE: moderate expenses ($40–$80K), $1M–$2M. Fat FIRE: high expenses ($100K–$300K+), $2.5M–$7.5M. Barista FIRE: part-time income + partial portfolio. Coast FIRE is a stage that can happen during any of these paths — it is a checkpoint, not a destination. The Fat FIRE calculator and Barista FIRE calculator model the other variants.
When Coast FIRE fails
Two scenarios. Market underperformance: your 7% assumption becomes 4%, and your portfolio grows slower than expected. Expense inflation: your assumed retirement expenses increase while portfolio growth assumes the original number. Both risks suggest building margin — if you need Coast FIRE at $200K, actually save to $250–$275K. If 7% might be optimistic, use 6% instead.
Getting to Coast FIRE as fast as possible
Three levers, in order of impact. Start early: someone starting at 22 needs roughly half the capital of someone starting at 32. Save aggressively during accumulation: not forever, just until Coast FIRE. 15–25% savings rates for 10–15 years often suffice. Reduce target expenses: planning for $60K instead of $90K cuts the target 33%.
This article is for educational purposes. It is not financial advice. Historical returns do not guarantee future outcomes. Consult a fee-only financial planner for decisions specific to your situation.