Coast FIRE Calculator

How to Use This Calculator

Enter your current age, how much you've already saved, and what you expect to spend in retirement. The calculator figures out your Coast FIRE number — the amount you need saved right now so that compound growth alone carries your portfolio to your retirement target, without another dollar contributed.

If your current savings are above the Coast FIRE threshold, congratulations — you've already reached Coast FIRE. If you're below it, the calculator shows you when you'll cross the line based on your current savings rate.

Here's what each field means:

Current Age is how old you are today. This determines how many years compound growth has to work.

Current Savings is everything you have invested toward retirement — 401(k), IRA, brokerage accounts, all of it.

Annual Spending in Retirement is what you expect to spend each year after you stop working. This is the foundation of your target portfolio calculation.

Target Retirement Age is when you want your portfolio to be fully funded for retirement. The default is 65, but you can set it earlier or later.

Safe Withdrawal Rate is the percentage of your portfolio you plan to withdraw each year in retirement. The classic 4% rule means you'd need a portfolio of 25 times your annual spending [1]. A more conservative 3.5% means you'd need roughly 29 times your spending.

Expected Return is the annual growth rate you expect from your investments. This should be a "real" return — after inflation. If you expect 10% nominal returns and 3% inflation, your real return is 7%.

Monthly Contributions is what you're currently saving each month. The calculator uses this to project when you'll cross the Coast FIRE threshold.

What Is Coast FIRE?

Coast FIRE is the point where you've saved enough money that you can stop contributing to your retirement accounts entirely — and your existing investments will grow to your retirement target on their own, thanks to compound interest.

Think of it like pushing a boulder to the top of a hill. Once it's at the top, gravity takes over. You don't need to push anymore. Coast FIRE is the top of the hill. Once you reach it, compound growth is the gravity that carries your portfolio the rest of the way.

This doesn't mean you can stop working altogether (that's full FIRE). It means you only need to earn enough to cover your current living expenses. You can stop stressing about your savings rate. Every dollar you earn goes toward living your life today, not funding a distant future.

The Math Behind Coast FIRE

The Coast FIRE number is calculated by taking your full retirement target and discounting it back to today using compound growth:

Coast FIRE Number = Retirement Target ÷ (1 + Real Return)^Years Until Retirement

Let's walk through an example. Say you want to spend $50,000 per year in retirement and plan to use the 4% rule. Your retirement target is:

$50,000 ÷ 0.04 = $1,250,000

Now, if you're 30 years old, planning to retire at 65, and expect a 5% real return, your Coast FIRE number is:

$1,250,000 ÷ (1.05)^35 = $226,575

That means if you have $226,575 invested at age 30 and never contribute another dollar, compound growth at 5% real return would grow it to roughly $1,250,000 by age 65.

Here's what makes this interesting: the younger you are, the lower the number. At 25 with 40 years until retirement, the same scenario gives you a Coast FIRE number of about $177,500. At 35, it jumps to $289,000. Every year you wait, the target climbs because there's less time for compounding to work.

Why Coast FIRE Matters

Coast FIRE isn't about quitting. It's about freedom.

Once you've crossed the threshold, every dollar you save beyond covering your expenses is a bonus. This changes the equation for a lot of people:

You could switch careers. Take that lower-paying job you've always wanted — teaching, nonprofit work, creative pursuits — without worrying that you're sacrificing your retirement.

You could go part-time. Work three days a week instead of five. Your retirement is funded regardless.

You could take a sabbatical. A year off to travel, write, spend time with kids, or recharge. Your investments keep compounding whether you're at a desk or on a beach.

You could stop optimizing your savings rate. No more spreadsheets tracking every dollar. You've already done the hard part. Now you can just... live.

For a lot of FIRE-minded people, Coast FIRE is the first big milestone. It's the moment you shift from "I must save aggressively" to "I'm going to be fine."

How the Chart Works

The calculator displays a chart with two key elements:

The Coast FIRE Threshold (rising curve) shows how much you'd need invested at each age to be on track. This line rises over time because as you get closer to retirement, there's less time for compound growth, so you need a larger starting balance.

Your Portfolio (projected line) shows your actual investment balance growing year by year. Once your portfolio crosses above the threshold line, you've reached Coast FIRE.

Before the crossover: you're in accumulation mode, saving and investing aggressively.

After the crossover: you're coasting. Your portfolio grows from investment returns alone, riding above the threshold line all the way to your retirement target.

Coast FIRE vs. Full FIRE

It's helpful to understand where Coast FIRE sits in the FIRE landscape:

Full FIRE means you can stop working entirely and live off your investments forever. Your portfolio is fully funded now, not at some future date.

Coast FIRE means your portfolio will be fully funded at retirement age without additional contributions. You still need income to cover your expenses until then — you just don't need to save any of it.

The practical difference is huge. Full FIRE for someone spending $50,000/year requires $1,250,000 saved today. Coast FIRE for a 30-year-old with the same target might require only $226,575. That's about 82% less.

This makes Coast FIRE accessible to people who might look at the full FIRE number and think "that's decades away." Coast FIRE could be just a few years away.

The Variable That Changes Everything: Time

Age is the most important input in this calculator. Here's why.

For someone targeting $1,250,000 at retirement with a 5% real return:

At 25, you need less than $178,000 to coast. At 50, you need over $600,000. Same retirement target, but the amount of time for compounding to work makes an enormous difference.

This is why the best time to invest aggressively is when you're young. A few years of intense saving in your 20s can set you up to coast for the rest of your career.

Limitations to Keep in Mind

Fixed returns are an assumption, not reality. This calculator assumes your investments grow at a steady rate every year. In practice, markets are volatile — some years you'll earn 20%, others you'll lose 15%. The sequence of those returns matters, especially as you approach retirement.

Inflation is built into the "real return" rate. If you entered a real return of 5%, that already accounts for inflation. Make sure you're not double-counting by also adjusting your spending target for inflation separately.

Life circumstances change. You might earn more (or less) than expected. Your spending needs might shift. Medical events, family changes, career pivots — all of these can change the equation. Revisit your numbers every year or two.

Coast FIRE doesn't mean zero risk. A severe bear market early in the coasting phase could push your portfolio below the threshold. Having a small buffer above the Coast FIRE number gives you cushion.

How to Use This Calculator Strategically

Find your crossover year. The most motivating number isn't the Coast FIRE amount — it's the year you hit it. If it's 3 years away instead of 15, that changes how you feel about your financial life.

Test different retirement ages. Moving your target from 65 to 60 raises the Coast FIRE number significantly. But pushing it to 70 drops it. See what feels right.

Play with the withdrawal rate. Using 3.5% instead of 4% increases your target but adds safety margin. Using 3% is very conservative but means a substantially larger portfolio requirement.

Model a career change. If you're at Coast FIRE, you could take a job paying $40,000 instead of $100,000 without jeopardizing retirement. Plug in those numbers and see what your life could look like.

References

1. Cooley, P., Hubbard, C., & Walz, D. (1998). Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable. AAII Journal.

This calculator is for educational purposes only and does not constitute financial advice. Actual investment returns vary, and past performance does not guarantee future results. Consider consulting a qualified financial advisor for personalized guidance.