What Is FIRE and Coast FIRE?

A plain-English introduction to FIRE (Financial Independence, Retire Early) and Coast FIRE — what the terms mean, how the 4% rule and the "multiply by 25" shortcut work, and the milestones between starting out and full independence.

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What FIRE actually means

FIRE stands for Financial Independence, Retire Early. Despite the name, it is less about quitting work at 40 and more about reaching the point where work becomes optional — where your investments can cover your living costs, so a paycheck is a choice rather than a necessity. People pursue it for very different reasons: some want to stop working entirely, others simply want the freedom to do work they find meaningful without worrying about the money.

At its core, FIRE combines two ordinary ideas and takes them seriously: spend meaningfully less than you earn, and invest the difference consistently so that compound interest does the heavy lifting over time. The higher the gap between what you earn and what you spend, the faster you get there. This guide explains the numbers behind FIRE and the milestones along the way — including a particularly freeing one called Coast FIRE, which you can size up with the Coast FIRE calculator.

Your FIRE number and the 4% rule

The central figure in FIRE is your FIRE number: the amount you need invested to live off your portfolio indefinitely. The most common way to estimate it comes from the 4% rule, a guideline drawn from historical market research suggesting that withdrawing about 4% of a portfolio in the first year of retirement, then adjusting for inflation, has a good chance of lasting a long retirement.

Flip that 4% around and you get a simple shortcut: multiply your annual expenses by 25.

• Spend $40,000 a year? Your FIRE number is roughly $1,000,000.
• Spend $60,000 a year? Roughly $1,500,000.
• Spend $80,000 a year? Roughly $2,000,000.

Two things fall out of this immediately. First, your FIRE number is driven by your spending, not your income — someone who lives on less needs a smaller portfolio to be free. Second, the 4% rule is a rule of thumb, not a law. It was based on particular historical periods and assumptions, and real outcomes depend on returns, inflation, taxes, and how long you need the money to last. Many people treat it as a starting estimate and adjust to be conservative.

The flavors of FIRE

Because “retire early” means different things to different people, a handful of variations have grown up around the core idea:

• Lean FIRE — reaching independence with a lower FIRE number by keeping expenses modest.
• Fat FIRE — a larger portfolio that supports a more comfortable, higher-spending lifestyle.
• Barista FIRE — partly there, with a part-time job that covers some expenses (and sometimes benefits) while your investments keep growing.
• Coast FIRE — the milestone this next section is about, and often the first one within reach.

What Coast FIRE means

Coast FIRE is one of the most encouraging milestones on the whole journey, because it arrives long before full independence. You reach Coast FIRE when you have already invested enough that, even if you never contribute another dollar, compounding alone will grow your balance to your full FIRE number by the time you retire.

You still need to cover today’s living costs out of current income. But the retirement piece is, in effect, taken care of on autopilot. You can stop investing for retirement and simply let the existing balance coast the rest of the way.

The reason this is possible is compound growth. A smaller amount today becomes a much larger amount after enough years, so the further you are from retirement, the smaller the Coast FIRE number needs to be. It is the same engine described in our compound interest guide, viewed from the other end: what seed, planted now, grows into the tree you need later?

A quick Coast FIRE example

Suppose you are 30, want to retire at 60, expect to spend $40,000 a year, and assume a 5% return after inflation. Your FIRE number is about $1,000,000 (that is $40,000 × 25). The Coast FIRE number — the amount that, left untouched, grows to a million over those 30 years — works out to a little over $230,000. If you already have that invested, you are coasting: you could stop retirement contributions today and still expect to arrive on schedule. If you have less, the gap tells you how much further you have to go. The Coast FIRE calculator runs these numbers for your own age, timeline, and expenses.

Why the milestone matters

Hitting Coast FIRE changes your options well before you are fully financially independent. Once your invested balance is coasting toward retirement on its own, you only need to earn enough to cover current expenses. That can open the door to a lower-stress job, part-time work, a career break, or taking a risk on something new — because the long-term piece is already handled. For a lot of people, that flexibility is the real prize, arriving years earlier than “retire early” ever could.

Keep the assumptions honest

FIRE and Coast FIRE both rest on assumptions that deserve respect: a steady return, stable spending, and a withdrawal rate that holds up over decades. Real markets are volatile, a poor run of early returns can change the picture, inflation erodes fixed numbers, and life plans shift. Treat these figures as motivating checkpoints and planning tools rather than guarantees.

This is general educational information, not financial advice. Whether FIRE makes sense for you, and what your numbers should be, depends on your own situation — and a qualified professional can help you pressure-test the plan. But understanding the milestones, especially Coast FIRE, can make the whole idea feel far less abstract and a good deal more reachable.