The Math To Reach CoastFIRE In Every Decade

Introduction – What Is Coastfire? (0:00)

Brian: What if you never had to save another penny? It sounds nice, right? That’s the idea behind Coastfire. And in this video, we’re going to show you what that means, how much you need, and how to get there in every stage of life. With that, let’s jump right in. Coastfire is a strategy where you save aggressively early on in life until you reach a specific portfolio value. Once you hit that target, you can stop saving entirely. Your existing investments continue to grow on their own until you reach retirement age, at which point you’ll have enough to retire comfortably. But with that definition comes a big question. How much do you need to hit Coastfire? The answer changes based upon where you start.

Key Assumptions (0:40)

Brian: And it depends on a few factors that can impact the math. First, before all the trolls crawl out from under the bridge and comment, “Hey, what about inflation, Brian?” We’re accounting for that. We’re going to assume an annual inflation rate of 2% which is the long-term target of the Federal Reserve. The income numbers we use from the Don’t Quit Your Day Jobs 2025 data will be inflation adjusted based upon how far they’re out from retirement. We’ll also assume replacing 80% of one’s pre-retirement income using a 4% withdrawal rate. These numbers are based on typical retirement income needs for most Americans and safe withdrawal rates backed by extensive portfolio research. The other implied assumption is that your income and lifestyle costs only increase with inflation. If your wage growth outpaces inflation or you upgrade your lifestyle, these numbers will need to be adjusted accordingly.

Coastfire at Age 25 (1:35)

Brian: Hitting Coastfire in your 20s. If you’re 25, the math is working heavily in your favor. The median income at this age is $45,000. When accounting for 2% inflation over the next 40 years, that number adjusts to $99,362 by age 65. If you’re trying to replace 80% of that income, it means you’ll need $79,489 per year in retirement. Using a 4% withdrawal rate, that puts your retirement number just under $2 million. To hit Coastfire today, you would need $45,126 invested. At this age, time is doing almost all of the heavy lifting. Four decades of compounding growth at 9.5% turns a relatively small starting balance into that full retirement portfolio of $1.99 million. Your biggest advantage in your 20s isn’t income. It’s all about your time. Saving early and often lets compounding do the heavy lifting, but only if lifestyle creep doesn’t steal that advantage before it ever shows up on your net worth statement.

Coastfire at Age 35 (2:45)

Brian: By age 35, income has typically increased with median earnings around $64,000. Adjusted forward for 30 years at 2% inflation, that becomes $115,927 at age 65. Planning to replace 80% of that income puts your retirement spending target near $92,742 per year. Applying a 4% withdrawal rate results in a total retirement goal of roughly $2.32 million. By your mid-30s, the window for ultra cheap compounding has narrowed, but time is still definitely on your side. That said, the portfolio has to start from a meaningfully higher base to reach the same destination. At age 35, you need about $182,670 invested, but growing at 8.5% annually. That portfolio can still reach your retirement target on its own. Your 30s are full of milestones. But every upgrade comes with a trade-off. The key isn’t avoiding life. It’s making sure short-term choices don’t permanently shrink the margin that keeps financial milestones within reach.

Coastfire at Age 45 (3:59)

Brian: At age 45, the timeline tightens and the math definitely shifts. Median income at this stage is about $70,000. After adjusting 20 years for inflation, that equals roughly $104,000 at age 65. Replacing 80% gives a retirement income goal of $83,213 per year. Using the 4% withdrawal rule, your total retirement number lands near $2 million. In your 40s, compounding still works, but it’s no longer forgiving, which means your Coastfire targets need to carry more of the load up front. At age 45, you need approximately $466,000 invested, assuming a 7.5% rate of return. That balance can compound to your full retirement number without further savings. In your 40s, the math gets stricter and the stakes get higher. Lower assumed returns reflect a real shift in risk tolerance, not pessimism. And aligning your portfolio with that reality is what keeps the plan intact.

Coastfire at Age 55 (5:05)

Brian: At age 55, Coastfire becomes more about preservation than acceleration. Median income here is $65,720, which adjusts to about $80,000 at age 65. Replacing 80% of that income means targeting roughly $64,000 a year in retirement spending. At a 4% withdrawal rate, your retirement portfolio needs to be about $1.6 million. At this stage, there’s very little room for growth to make up for underfunding. So, the Coastfire number needs to be much closer to the finish line from day one. You need around $838,000 invested at age 55, assuming a conservative 6.5% return. That portfolio can still grow to your retirement number by age 65 without additional contributions. Your 50s are about clarity and commitment. Being honest about where you stand today allows you to adjust expectations and stay focused because Coastfire at this stage is less about optimization and more about finishing strong.

Closing – Personal Finance Is Personal (6:11)

Brian: While personal finance is personal and these numbers definitely should be tailored to you, the exercise builds clarity and Coastfire isn’t a finish line. So keep checking your plan and saving beyond the minimum to create margin and flexibility. If you want to know more about the various levels of wealth, I want you to click right here. And as always, keep building towards your great big beautiful tomorrow.