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What Is Coast FIRE? How Existing Savings Can Carry You to Retirement

What it means, where the term came from, how the math works, and the risks to plan for.

By J.J. Allan LLC · Published October 15, 2026 · About 9 min read

Coast FIRE is the point at which the money you have already invested for retirement is large enough that, if you never contributed another dollar, ordinary investment growth would carry it to your full retirement target by the age you plan to retire. You still work to cover today's living costs. What changes is that you no longer have to save for retirement. The heavy lifting has been done, and time does the rest.

That shift sounds modest, but it changes the economics of a career. Once retirement saving is optional, a lower-paying role, a sabbatical, a business launch or simply higher present-day spending stops being a threat to your long-term security. This guide explains where the idea came from, how the math works, how it compares with other forms of FIRE, who it suits, and the risks worth taking seriously. If you'd like to see your own numbers first, the Coast Clock Calculator estimates when your savings could start coasting.

The short definition

FIRE stands for Financial Independence, Retire Early. Classic FIRE aims to build a portfolio large enough to live on now, usually about 25 times annual spending. (For background on that target and the research behind it, see our guide, What Is FIRE?)

Coast FIRE borrows the same end target but asks a different question. Instead of "Do I have enough to stop working?" it asks: "Do I have enough that it will become enough, on its own, by the time I want to stop?" Some writers call it Coast FI and drop the "retire early," because most people who reach it keep working, often for decades. The early part is the freedom from mandatory saving, not early retirement itself.

Where the term came from

Unlike FIRE, which can be traced to a specific 1992 book and a handful of 1990s research papers, Coast FIRE has no clearly documented inventor. We were not able to find a reliable source identifying who first coined the term, and we'd rather say so than repeat an unverified origin story.

What can be verified is that it grew out of online FIRE communities in the 2010s. By 2018, members of Reddit's FIRE forums were already debating how "Coast FIRE" differed from "Barista FIRE," which suggests the label was in circulation before then. In October 2020, WalletBurst published a widely shared "complete guide" to Coast FIRE along with a free calculator; its author noted at the time that there wasn't much detailed content on the topic. Since then, mainstream outlets including Forbes, NerdWallet, Fortune and Investopedia have explained the concept for general audiences.

The underlying idea is much older than the name. Compound growth has been central to retirement planning for generations, and financial planners have long told clients that money invested early does more work than money invested late. Coast FIRE packages that principle into a specific, measurable milestone.

How the math works

Coast FIRE rests on two calculations: the size of the portfolio you'll eventually need, and how much you need today for growth to get you there.

Step 1: Your FIRE number

Your full target is your expected annual retirement spending divided by a withdrawal rate:

FIRE number = annual retirement spending ÷ withdrawal rate

At the commonly used 4% rate, that works out to 25 times annual spending. The 4% figure traces to William Bengen's 1994 research and the 1998 Trinity Study, both of which tested withdrawals against historical U.S. market returns. Many planners now treat 4% as a starting point rather than a guarantee, and some early retirees use 3.5% or lower to build in a margin of safety.

Step 2: Your Coast FIRE number

Next, work backward from that target. If your investments grow at a real (after-inflation) annual return r for n years until retirement, the amount you need today is:

Coast FIRE number = FIRE number ÷ (1 + r)ⁿ

Using a real return keeps everything in today's dollars, so you don't have to forecast inflation separately. The Coast Clock Calculator and several widely used calculators take the same approach: they adjust expected returns for inflation and work in present-day purchasing power.

A worked example (illustrative only)

Consider a hypothetical 35-year-old who expects to spend $60,000 a year in retirement (in today's dollars) and plans to retire at 65, 30 years from now.

If this person already has about $347,000 invested and it earns a 5% real return on average, it would grow to roughly $1.5 million by 65 without any further contributions. From that point, their paycheck only needs to cover current living costs.

The assumed return matters a great deal. Holding everything else constant:

Time matters just as much. At 5%, the same $1.5 million target requires about $443,000 with 25 years to go, and about $565,000 with 20 years to go. The earlier you reach your number, the less of it you have to supply yourself.

These figures are illustrative, not projections or recommendations. Actual returns vary year to year, and an average return over 30 years can hide long stretches of poor performance.

To run the same calculation with your own age, savings and spending, use the Coast Clock Calculator.

How Coast FIRE compares with other types of FIRE

The FIRE community uses several labels for different targets and lifestyles. They overlap, and none is official, but the distinctions are useful.

In practice, these milestones often happen in sequence. Many people reach Coast FIRE well before they reach full FIRE, and some decide that coasting is the goal they actually wanted all along.

Who Coast FIRE is for

Coast FIRE tends to suit people who:

It's less useful for people who are early in their saving journey or late in their careers. If you have little invested or only a few years until retirement, compound growth has less to work with, and steady contributions remain the main lever.

Common misconceptions

"Coast FIRE means retiring early." It usually doesn't. Most people who reach Coast FIRE keep working; they simply stop being obliged to save. The freedom comes from what your paycheck no longer has to do.

"Once you hit the number, you're done forever." The number is a projection, not a finish line. A market downturn shortly after you stop contributing, a change in spending plans or a lower-than-expected return can push you back below it. It's worth rechecking at least once a year.

"You can stop working entirely." Coast FIRE assumes you continue to earn enough to cover current living expenses until retirement. If you stop earning altogether and start drawing on the portfolio, you're no longer coasting, and the math changes.

"Any balance in a retirement account counts the same way." Taxes matter. A dollar in a traditional 401(k) or IRA will be taxed when withdrawn, while a dollar in a Roth account generally won't be. Your spending figure should account for the taxes you expect to owe in retirement.

"Higher return assumptions are harmless." Small changes compound into large differences. As the example shows, moving from 5% to 7% cuts the required balance by more than 40%. Optimistic assumptions make the milestone look closer than it is.

Risks and caveats

Sequence of returns. Markets don't deliver averages smoothly. A long bear market early in your coasting years can leave your portfolio well behind schedule, and without new contributions there is nothing to buy in at lower prices.

Withdrawal-rate uncertainty. The 4% rule was developed largely for 30-year retirements using historical U.S. data. If you plan to retire earlier or expect lower future returns, a more conservative rate, and therefore a larger target, may be prudent.

Healthcare and other large costs. In the U.S., Medicare generally begins at 65. A coaster who changes jobs or works part-time may lose employer coverage, and the cost of replacing it belongs in the present-day budget.

Social Security and pensions. Some people reduce their target to account for expected Social Security or pension income. That can be reasonable, but benefits depend on your earnings history and claiming age; claiming at 62 permanently reduces them compared with waiting until full retirement age. Use your own benefit estimate rather than a rule of thumb. In the Coast Clock Calculator, please don't do this by lowering your annual spending: that field also sets how much you save today, so the benefit would be counted twice. We don't model retirement income separately yet, so the calculator's result is the cautious version.

Life changes. Children, caregiving, divorce, disability and shifting goals all affect long-range plans. Coast FIRE buys flexibility, but it works best with an emergency fund and a willingness to resume saving if circumstances change.

The bottom line

Coast FIRE turns compound growth into a concrete milestone: the point at which your past saving has done enough that your future self is covered, provided the assumptions hold. It doesn't require retiring early or living frugally forever. It requires saving meaningfully early on, choosing realistic assumptions and revisiting them as life unfolds.

For many professionals, that milestone is more achievable and more useful than full early retirement. It turns retirement saving from an obligation into a choice and opens up career and lifestyle options that would otherwise feel risky. To find out where you stand, visit Coast Clock or go straight to the Coast Clock Calculator and find your coast age.

Further reading

If you want one book on the investing side of reaching and holding a coast point, J.L. Collins's The Simple Path to Wealth is a good place to start. It makes a plain-spoken case for simple, low-cost index fund investing and avoiding debt, the approach much of the FIRE community relies on.

Coast FIRE is as much about deciding what is enough as it is about the numbers. Vicki Robin and Joe Dominguez's Your Money or Your Life, the book that helped start the FIRE movement, is built around that question, and it pairs well with the idea of letting your savings coast while work becomes a choice.

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This article is for general education only and is not financial, tax or legal advice. Withdrawal rates, returns and tax rules vary, and past market performance doesn't guarantee future results. For decisions about your own money, consult a licensed financial professional.

Sources

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