Coast FIRE Explained: Calculate Your Number and Stop Saving Forever
Coast FIRE Explained: Calculate Your Number and Stop Saving Forever
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I still remember the exact moment I ran the numbers for the first time.
I was sitting in my car in the hospital parking lot, still in scrubs after a 12-hour shift, plugging figures into my phone calculator. I’d been maxing my 401(k) for years, and I wanted to know where I actually stood.
When the result came up, I had to reread it twice.
I had already crossed my Coast FIRE number.
Not my full FIRE number — I wasn’t done working yet. But the math said something I hadn’t expected: I could stop contributing to retirement accounts entirely, coast on what I’d already saved, and still hit my target by 65.
Here’s what I wish someone had told me years earlier: for many diligent savers, Coast FIRE isn’t some distant dream. You may be closer — or already there — and not even know it.
Quick Summary
– Coast FIRE = having enough invested today that compound growth alone will reach your retirement target, with no additional contributions required
– The formula: Coast FIRE Number = FIRE Number ÷ (1.07)^years_until_retirement
– Once you hit it, you only need income to cover your current living expenses — not to save for the future
– A 25-year-old targeting $1.5M by 65 only needs roughly $81,000 invested today
– The earlier you start, the lower your Coast FIRE number — time is doing most of the work
What Is Coast FIRE?
Coast FIRE is a specific milestone within the broader FIRE (Financial Independence, Retire Early) movement. The idea is simple: you’ve invested enough money that, if you leave it completely alone, compound growth will carry it to your full retirement target by the time you want to retire.
No new contributions. No aggressive saving. Just time and compounding doing their thing.
The word “coast” is intentional. Once you hit this number, you’re coasting — like a cyclist who’s powered up the hill and can now freewheel down the other side. You still need income to pay for your life right now. But you no longer need to sacrifice today’s income for tomorrow’s retirement.
This is different from traditional FIRE, where the goal is to accumulate enough that you can live entirely off investment returns now. Traditional FIRE requires a much larger nest egg because you’re withdrawing from it immediately.
With Coast FIRE, you’re not touching the invested money. You’re just letting it grow. The freedom it gives you isn’t “I never have to work again” — it’s “I never have to stress about saving for retirement again.” That’s a different kind of freedom, and for a lot of people, it’s enormously meaningful.
r/financialindependence has surpassed 700,000 members, and surveys consistently show that roughly 25% of Gen Z plans to retire before 55. Coast FIRE is one of the most accessible on-ramps to that goal — because the number you need is dramatically lower than full FIRE.
The Coast FIRE Formula (It’s Simpler Than You Think)
The math here is honest and not complicated. Two inputs feed into it.
Step 1: Your FIRE Number
Your FIRE Number is the total portfolio value you’d need to retire fully today, using the 4% safe withdrawal rate rule. The formula:
FIRE Number = Annual Spending ÷ 0.04
If you spend $60,000 per year, your FIRE Number is $1,500,000.
(Need help finding your FIRE Number? I break it down fully here.)
Step 2: Coast FIRE Number
Now you discount that future target back to what you’d need today to reach it, assuming a 7% real annual return (meaning after inflation):
Coast FIRE Number = FIRE Number ÷ (1 + 0.07)^years_until_retirement
A real example:
Say you’re 30 years old, you plan to retire at 65, and your target is $1,500,000.
$1,500,000 ÷ (1.07)^35 = $1,500,000 ÷ 10.68 = ~$140,000
If you have $140,000 invested at 30 and never add another dollar, compound growth at 7% real should carry that money to roughly $1.5 million by the time you’re 65.
The numbers don’t lie: that’s a reachable number for a lot of people who’ve been contributing to a 401(k) for several years.
On the 7% assumption: this is a commonly used real (inflation-adjusted) return estimate for a diversified stock index portfolio, based on long-run historical U.S. market data. It’s not guaranteed, and your actual returns will vary. I use it because it’s the most common baseline in FIRE planning — but be aware that conservative planners sometimes use 5% or 6% for a wider margin of safety.
How Much Do You Need to Coast FIRE? (By Age)
This table assumes a $1,500,000 target FIRE number (annual spending of $60,000 at a 4% withdrawal rate) and a 7% real annual return. Use it as a rough benchmark — your personal number will vary based on your actual spending and retirement age.
| Current Age | Years to 65 | Coast FIRE Number |
|---|---|---|
| 25 | 40 | ~$81,000 |
| 30 | 35 | ~$114,000 |
| 35 | 30 | ~$160,000 |
| 40 | 25 | ~$225,000 |
| 45 | 20 | ~$316,000 |
| 50 | 15 | ~$444,000 |
Notice how dramatically the number rises with age. At 25, you need about $81,000. At 45, you need nearly four times that. Every year you delay, the Coast FIRE number goes up because compound growth has less time to work.
This is one of the most powerful arguments for starting early — not so you can contribute more, but so your contributions can compound longer.
To adjust for your own spending: if your annual spending is different from $60,000, scale proportionally. If you spend $40,000/year, your FIRE Number is $1,000,000, and your Coast FIRE numbers are about two-thirds of what’s shown above. If you spend $80,000/year, add roughly one-third.
Coast FIRE vs. Traditional FIRE vs. Barista FIRE
These three terms get conflated. Here’s how they actually differ:
| Traditional FIRE | Coast FIRE | Barista FIRE | |
|---|---|---|---|
| Core goal | Full financial independence; never work again | Retirement savings are “done”; still work for living expenses | Partial retirement; part-time work covers expenses AND benefits |
| Portfolio needed | Full FIRE number (e.g., $1.5M) | Coast FIRE number (e.g., $160,000 at 35) | Less than full FIRE; bridge built by income |
| Work after? | Optional | Yes — for living expenses | Yes — part-time by design |
| Benefits coverage | Self-funded | Self-funded | Often covered by employer (e.g., Starbucks, REI) |
| Best for | People who want complete work-optionality now | People okay with working but want retirement stress gone | People who want flexibility AND employer health coverage |
Barista FIRE is often confused with Coast FIRE, but there’s a key distinction: in Barista FIRE, the part-time job is specifically chosen to provide health insurance and cover living costs — you’re not fully relying on your investments yet. In Coast FIRE, your investments are already on autopilot for retirement; you’re just working to fund your present life.
Neither is better. They’re different tools for different situations.
How to Calculate Your Personal Coast FIRE Number (Step by Step)
Let me walk through this with real numbers — mine, from when I first did this calculation.
Step 1: Determine your annual spending
Be honest here. Include everything: housing, food, transportation, healthcare, travel, fun. Underestimating is the most common Coast FIRE mistake.
My number at the time: $58,000/year
Step 2: Calculate your FIRE Number
FIRE Number = Annual spending ÷ 0.04
$58,000 ÷ 0.04 = $1,450,000
Step 3: Determine years until your target retirement age
I was 34, targeting retirement at 55.
55 − 34 = 21 years
Step 4: Apply the Coast FIRE formula
Coast FIRE Number = $1,450,000 ÷ (1.07)^21
(1.07)^21 ≈ 4.14
$1,450,000 ÷ 4.14 = ~$350,000
Step 5: Compare to your current portfolio
When I ran this at 34, I had about $380,000 across my 401(k) and Roth IRA.
I had already passed my Coast FIRE number.
That doesn’t mean I stopped working or stopped caring about money. But it completely changed how I thought about my career. I stopped feeling trapped. I started thinking about whether I actually wanted to keep doing 12-hour shifts, versus what else I might build. That mental shift was worth everything.
What Happens After You Hit Coast FIRE?
This is where people get tripped up.
Hitting Coast FIRE does not mean you can stop working. It means you can stop contributing to retirement accounts. You still need income to cover your living expenses today.
Here’s what that might look like in practice:
- Keep your current job but reduce stress. You’re no longer chained to a high-income job to fund retirement savings. A job that pays 30% less might be perfectly fine if it covers your expenses.
- Shift to part-time or consulting. Many Coast FIRE people work 20–30 hours a week in a lower-pressure role, covering their bills without the weight of retirement contributions.
- Build a side income. A small freelance practice, rental income, or online business can cover living expenses without requiring a full-time W2 grind.
- Barista FIRE as a bridge. If you need health insurance, a part-time employer that provides benefits is a practical bridge between Coast FIRE and full retirement.
The key distinction: you are still working. The investment portfolio is on a separate track, growing untouched.
The Mistakes People Make With Coast FIRE
When I first hit this milestone, I almost made a few of these mistakes myself.
1. Ignoring inflation in your spending estimate
Your $60,000/year lifestyle today will cost more in 30 years. The 7% real return assumption accounts for inflation in the portfolio, but your spending needs to be estimated in today’s dollars accurately. Underestimate spending now, and the Coast FIRE number comes out too low.
2. Not accounting for healthcare
This is the one that blindsides people, especially if they’re used to employer-sponsored coverage. Healthcare costs between early retirement and Medicare eligibility (age 65) can be substantial. If you’re planning to Coast FIRE and reduce your hours, make sure you’ve modeled healthcare costs honestly — either through an employer, the ACA marketplace, or a health-sharing arrangement.
3. Stopping contributions too early
Coast FIRE math assumes a single investment amount growing untouched. If you stop saving and then dip into the account for an emergency, the compounding projection breaks. Build an emergency fund before you let yourself coast. Don’t confuse “stop contributing to retirement” with “stop saving entirely.”
4. Using an overly optimistic return rate
7% is a reasonable long-run estimate, but markets don’t move in a straight line. If you’re using 8% or 9% to make your current number work, you’re taking on meaningful risk. I’d rather see you use 6% and arrive at 65 with more than you planned.
5. Forgetting Social Security
For most people, Social Security will cover some portion of retirement spending. If you account for it, your required FIRE Number — and therefore your Coast FIRE Number — is lower. This is a margin-of-safety item: I’d calculate your Coast FIRE number without Social Security, and treat Social Security as a buffer.
How to Accelerate to Your Coast FIRE Number
The faster you reach Coast FIRE, the sooner the compounding clock starts. Here’s what actually moves the needle.
Max tax-advantaged accounts first
Your 401(k), Roth IRA, and HSA are the highest-leverage vehicles for reaching Coast FIRE quickly because they grow tax-advantaged. A dollar in a Roth IRA compounds without being taxed on the way out. A dollar in an HSA is triple tax-advantaged.
- How your 401(k) reduces your taxes — this is the mechanism most W2 employees underuse
- The HSA triple tax advantage — if you have access to a high-deductible health plan, this is worth reading
- Investment order of operations — the sequence that maximizes your after-tax compounding
Invest in low-cost index funds
Expense ratios are a direct drag on compounding. A 1% expense ratio versus 0.04% (Vanguard or Fidelity total market index funds) costs you roughly 25% of your ending portfolio over 30 years. Use broad index funds through a low-cost brokerage. Both Fidelity and Vanguard offer index funds with some of the lowest expense ratios in the industry — Fidelity’s FZROX has a 0% expense ratio.
Increase your savings rate, even temporarily
You don’t need to sustain an aggressive savings rate forever. A few high-income years early in your career, funneled aggressively into index funds, can get you to Coast FIRE ahead of schedule. Then you can dial back.
Reduce spending strategically
The math works in both directions: lower spending means a lower FIRE Number, which means a lower Coast FIRE Number. Spending $50,000/year instead of $70,000 cuts your required Coast FIRE Number by nearly 30%.
Frequently Asked Questions
Does Coast FIRE account for inflation?
When we use 7% as the “real” return rate, inflation is already baked in — it’s 7% above inflation. So the Coast FIRE Number is expressed in today’s dollars, and the math already assumes your money keeps pace with inflation and then some. What you do need to account for is whether your spending estimate today is accurate in real terms.
Should I include home equity in my Coast FIRE number?
Generally, no. Home equity is illiquid and your home is not a cash-flowing asset while you live in it. Your Coast FIRE calculation should be based on liquid, invested assets — 401(k), Roth IRA, taxable brokerage, HSA. You can count home equity as a buffer or an emergency option, but don’t lean on it as your primary calculation input.
What about Social Security?
Social Security will reduce how much your portfolio needs to cover in retirement. If you expect $1,500/month from Social Security, that’s $18,000/year off your annual spending requirement — which meaningfully reduces your FIRE Number and, therefore, your Coast FIRE Number. I calculate Coast FIRE conservatively without Social Security, and treat it as a bonus. If you’re closer to retirement, you can factor it in more precisely.
What return rate should I use?
7% real (inflation-adjusted) is the most commonly used estimate in FIRE planning, based on long-run historical stock market returns. Conservative planners use 5–6%. I wouldn’t go above 7% for planning purposes — you want your reality to beat your projection, not fall short of it. If you want to be conservative, run the numbers at 6% and treat 7% as your optimistic scenario.
Can I still Coast FIRE in my 40s?
Yes. It’s harder because compounding has less runway, but it’s absolutely achievable. A 45-year-old targeting $1.5M by 65 needs about $316,000 invested. If you’re 45 and have $200,000, you’re not there yet — but you might be much closer than you think. And every dollar you add now has 20 years to compound. Don’t let the higher number discourage you from the math.
Bottom Line
Coast FIRE is the most underrated milestone in personal finance.
It doesn’t require you to quit your job, move somewhere cheap, or live off bean soup. It just requires enough invested, early enough, that time and compounding can take over the heavy lifting.
The numbers don’t lie: at 25, you might need as little as $81,000. At 35, around $160,000. These are numbers that years of diligent 401(k) contributions can reach — and some of you reading this have already crossed them without realizing it.
Your action step today: calculate your Coast FIRE number. Take your annual spending, divide by 0.04 to get your FIRE Number, then divide that by (1.07) raised to the power of your years until retirement. Compare that to what you have invested right now.
You might be further along than you think.
If you want a framework for what to do once you’ve calculated your number — and how to sequence your savings to get there faster — the investment order of operations is the next thing to read.
And if you want articles like this delivered straight to your inbox — real numbers, no fluff — join the Aedilis newsletter below. I write for W2 employees who are serious about building wealth on their own terms.
Legal Disclaimer: This article is for informational and educational purposes only. It does not constitute financial, tax, or investment advice. Individual circumstances vary significantly. Consult a qualified financial advisor before making any investment decisions. Past market performance does not guarantee future results. The 7% real return assumption is a historical estimate and not a prediction of future returns.
