What Is Coast FIRE? How to Know If You Can Stop Saving

Imagine reaching a point where you could stop adding a single dollar to your retirement accounts, keep working just enough to cover your bills, and still retire comfortably on schedule. That's not wishful thinking; it's a milestone the financial independence community calls Coast FIRE. It's one of the most freeing numbers in personal finance because it tells you the exact moment compound interest can take over the heavy lifting.

This guide explains what Coast FIRE is, how it differs from regular (full) FIRE and Barista FIRE, the simple discount-back-to-today formula that powers it, and a fully worked example in 2025 dollars. By the end you'll know how to check whether you've already hit your own Coast FIRE number, or how far away it is.

This article is for general informational and educational purposes only and is not professional financial advice. Consult a qualified financial advisor about your specific situation.

What Coast FIRE Actually Means

FIRE stands for Financial Independence, Retire Early. The classic version means saving aggressively until your portfolio is large enough to live on indefinitely. Coast FIRE is a gentler, earlier milestone along that same road.

You reach Coast FIRE when you have enough money already invested that, with zero additional contributions, it will grow on its own to your full retirement number by the time you actually retire. The money simply "coasts" the rest of the way, powered entirely by compound growth.

The catch is that you still need to cover your living expenses until retirement. So Coast FIRE doesn't mean you stop working; it means you stop saving for retirement. Your paycheck now only has to handle today's life, not tomorrow's. That can free you to:

• Switch to a lower-stress or lower-paying job you actually enjoy.
• Go part-time, freelance, or take a sabbatical.
• Redirect future savings toward a house, travel, or starting a business.
• Simply breathe easier knowing retirement is already handled.

The key insight is that the earlier you front-load your investing, the more years compounding has to work, and the smaller the lump sum you need today. Time, not just money, is doing the work.

First, Find Your FIRE Number (The 4% Rule)

Before you can calculate Coast FIRE, you need your FIRE number, the total portfolio you'd need to retire fully. The standard shortcut is the 4% rule, based on the well-known Trinity Study, which suggests you can safely withdraw about 4% of your portfolio in your first year of retirement and adjust for inflation thereafter, with a high probability the money lasts 30+ years.

Flip that 4% around and you get a clean formula:

FIRE Number = Annual Retirement Spending × 25

Multiplying by 25 is just the math equivalent of dividing by 4% (since 1 ÷ 0.04 = 25). A few examples:

Be honest about your spending, not your income. The number that matters is what you'll actually spend per year in retirement, including healthcare and the occasional splurge. Some cautious savers use a 3.5% withdrawal rate instead (multiply by ~28.6) for an extra safety margin, especially if they're retiring very early.

The Coast FIRE Formula: Discounting Back to Today

Here's the elegant part. Once you know your FIRE number, you work backward to figure out how much you'd need invested right now so it grows into that number by retirement, with no new contributions. This is called discounting to present value.

The formula is:

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

where:

• r = your expected real annual return (return after inflation), expressed as a decimal.
• n = the number of years until you plan to retire.

That (1 + r)ⁿ term is your compound growth multiplier. Dividing your FIRE number by it tells you the lump sum that, left completely alone, compounds up to your target. If your current invested balance equals or exceeds this Coast FIRE number, congratulations, you can technically stop saving for retirement.

Rather than do this by hand every time, you can plug your figures into our Coast FIRE Calculator, which discounts your target back to today instantly and tells you whether you've crossed the line.

Why You Must Use Real (Inflation-Adjusted) Returns

The single most important assumption in this whole calculation is your return rate, and the most common mistake is using a nominal number like 10%.

Historically, the U.S. stock market has returned roughly 10% per year nominally, but inflation has averaged around 3%. The difference, about 7%, is your real return, the growth in actual purchasing power. Because your FIRE number is in today's dollars, you must discount using a real return so you're comparing apples to apples.

If you mistakenly use 10%, the calculator will tell you that a much smaller amount today will "reach" your goal, but that future balance would be eroded by decades of inflation and wouldn't actually buy the lifestyle you planned. A conservative, realistic real-return assumption is typically 5% to 7%. We'll use 7% in the example below, but running 5% and 6% as well is a smart way to stress-test your plan.

A Fully Worked Example

Meet Taylor, a 30-year-old who plans to retire at 65, giving compounding 35 years to work. Taylor expects to spend $60,000 per year in retirement (in today's dollars) and will use a 7% real return assumption.

Step 1 - Find the FIRE number.

• $60,000 × 25 = $1,500,000

Step 2 - Calculate the compound multiplier for 35 years at 7%:

• (1.07)³⁵ ≈ 10.677

Step 3 - Discount the FIRE number back to today:

• $1,500,000 ÷ 10.677 ≈ $140,490

So Taylor's Coast FIRE number is about $140,500. If Taylor has roughly $140,500 invested today and never adds another cent, it should grow to about $1.5 million by age 65, enough to retire on the 4% rule. Here's how that single lump sum compounds over time:

Notice how the growth accelerates. The balance barely doubles in the first decade but adds over half a million dollars in the final decade alone, that's compounding's famous hockey-stick curve. It's also why hitting Coast FIRE young is so powerful: the same $140,500 invested at age 40 instead of 30 would only grow to about $762,000 by 65, less than half as much, because it lost ten of its best compounding years.

Notice, too, how sensitive the number is to time. If Taylor wanted to retire at 55 (only 25 years out), the multiplier drops to (1.07)²⁵ ≈ 5.427, so the Coast FIRE number jumps to about $276,400, nearly double. Fewer years means compounding does less, so you need more upfront. You can model all of these scenarios with our Compound Interest Calculator to see exactly how each assumption moves the target.

Coast FIRE vs Full FIRE vs Barista FIRE

Coast FIRE is one of several flavors in the FIRE family. Here's how the main types compare:

The practical difference between Coast and Barista FIRE: with Coast FIRE, your job covers all your current living costs, but you no longer save anything for retirement. With Barista FIRE, you're already drawing some income from your portfolio and just need a smaller paycheck to fill the gap. Coast FIRE typically comes first on the journey; Barista and full FIRE come later.

How to Check If You've Hit Coast FIRE

The process is straightforward:

• Estimate your annual retirement spending in today's dollars, healthcare and all.
• Multiply by 25 to get your FIRE number (or by ~28.6 for a cautious 3.5% rate).
• Pick a real return you believe in, 5% to 7% is a sensible range.
• Count the years until your target retirement age.
• Divide your FIRE number by (1 + r)ⁿ to get your Coast FIRE number.
• Compare it to your current invested balance. If you're at or above it, you've coasted. If not, the gap tells you how much more to invest.

One important note: only count money that's actually invested for retirement, your 401(k), IRA, and taxable brokerage holdings. Your emergency fund, checking account, and home equity don't belong in this calculation because they aren't compounding toward your retirement target. To project your workplace balance specifically, our 401(k) Calculator can show how your current contributions and employer match build toward (and past) your Coast FIRE number.

Common Mistakes to Avoid

• Using nominal returns instead of real returns. Plugging in 10% instead of 7% makes your Coast FIRE number look far smaller than it really is and ignores inflation entirely. Always discount in today's dollars.
• Lowballing retirement spending. Forgetting healthcare, taxes, or lifestyle creep gives you a FIRE number that's too small. Be realistic and slightly conservative.
• Forgetting you still have to live. Coast FIRE only stops your retirement saving. You still need income for rent, food, and the unexpected, so don't quit working entirely until you hit full FIRE.
• Ignoring sequence and market risk. Compounding isn't a smooth 7% every year. A bad stretch right before retirement can dent the plan, so revisit your numbers regularly rather than setting and forgetting.
• Dropping retirement contributions too aggressively. Just because you can stop saving doesn't always mean you should. Continuing to invest a little builds a safety buffer and can pull your full-FIRE date much closer.
• Skipping a stress test. Run the math at 5%, 6%, and 7% real returns. If the plan only works at an optimistic 7%, it's fragile.

The Bottom Line

Coast FIRE is the milestone where your invested money becomes a self-sufficient engine, growing into your full retirement number with no further contributions. The math is simple: find your FIRE number (annual spending × 25), then discount it back to today using a realistic real return over the years until retirement. If your current portfolio meets that discounted figure, you've hit Coast FIRE and earned the freedom to stop saving and start living more on your terms.

Because it rewards investing early, Coast FIRE is one of the strongest arguments for front-loading your retirement accounts in your 20s and 30s. Run your own numbers with our Coast FIRE Calculator, project your accounts with the 401(k) Calculator, and model different return assumptions with the Compound Interest Calculator. You may be closer to coasting than you think.