Coast FIRE Explained: How to Calculate Your Number

Most FIRE strategies demand years of aggressive saving and investing. Coast FIRE flips the script. It asks a simpler question: how much do I need to have invested right now so that I never need to save another dollar and still retire on time?

If you've ever fantasized about downshifting to a lower-paying job, taking a sabbatical, or just loosening your budget without torpedoing your retirement plan, Coast FIRE is the concept that makes that math concrete.

What Coast FIRE Actually Means

Coast FIRE is the portfolio balance at which compound growth alone—with zero additional contributions—will carry you to your full FIRE number by a target retirement age. Once you cross this threshold, you still need income to cover your current living expenses, but you no longer need to save a single dollar for retirement.

Think of it as a milestone, not a destination. You haven't retired. You haven't even reached financial independence. But you've bought yourself something valuable: the freedom to stop optimizing your savings rate and start optimizing your life.

The Math Behind Coast FIRE

The core formula is straightforward. You take your FIRE number and discount it back to the present using an assumed real (inflation-adjusted) rate of return:

Coast FIRE Number = FIRE Number / (1 + real return rate)^{years until retirement}

Let's walk through a concrete example. Suppose:

• Your FIRE number is $1,500,000
• You want to retire at age 60
• You're currently 30 years old (so 30 years until retirement)
• You assume a 6% real return on your investments

Plugging in: $1,500,000 / (1.06)³⁰ = $1,500,000 / 5.7435 = ~$261,000.

That's it. If a 30-year-old has roughly $261,000 invested today, and the market delivers 6% real returns over the next three decades, they'll land at $1.5 million by 60 without contributing another cent.

The younger you are, the smaller the number. A 25-year-old with the same assumptions would need only about $195,000. A 40-year-old would need roughly $470,000. Time is the most powerful variable in this equation.

The Assumption Problem

Here's where Coast FIRE gets tricky. The formula hinges on a single assumed rate of return, and small changes to that assumption produce dramatically different results:

At 7% real returns, Coast FIRE looks almost easy for someone who started saving in their twenties. At 4%, it's a much heavier lift. The difference between those two assumptions is more than $265,000—a gap that could represent years of additional saving.

This is the fundamental weakness of any Coast FIRE calculator that uses a single fixed return rate. The future won't deliver a steady 6% every year. It will deliver a volatile sequence of gains and losses that might average out to 6%, or might not. That's why Monte Carlo simulation—which tests your plan against hundreds or thousands of possible market scenarios drawn from actual historical data—gives you a much more honest picture than a single-number formula ever can.

Coast FIRE vs. Barista FIRE

You'll often see Coast FIRE and Barista FIRE used interchangeably, but there's a useful distinction. Both assume you've saved enough to let compound growth handle retirement. The difference is in what comes next:

• Coast FIRE is primarily a mathematical milestone. You've hit a number. What you do with that knowledge—keep working full-time, cut back, change careers—is up to you.
• Barista FIRE specifically emphasizes switching to part-time or lower-stress work, often with a focus on getting employer-sponsored health insurance (hence the “barista” name, referencing companies like Starbucks that offer benefits to part-time employees).

In practice, Coast FIRE is the calculation, and Barista FIRE is one lifestyle that flows from it. Neither is a separate FIRE strategy in the way that lean FIRE or fat FIRE are. They're waypoints on the same journey.

Who Coast FIRE Is For

Coast FIRE resonates most with three groups of people:

The Burned-Out High Earner

You're in a demanding career—tech, finance, medicine, law—and you've been saving aggressively for years. You don't hate working, but you hate this work at this intensity. Coast FIRE gives you a concrete number that says: you can take the lower-paying job, the nonprofit role, the freelance gig. Your retirement is already funded.

The Early Starter

You began investing at 22, and now at 30 you've accumulated more than most people your age. Coast FIRE validates what compound interest has already done for you and gives you permission to redirect your savings toward travel, education, or experiences without guilt.

The Psychologically Exhausted Saver

You've been grinding toward a FIRE number that feels impossibly far away. Coast FIRE reframes the problem. Instead of focusing on the $1.5 million finish line, you focus on a $261,000 milestone that might be within reach this year or next. It's a psychological unlock as much as a financial one.

The Risk You're Taking

Coast FIRE is a bet on decades of compound growth. That bet is historically well-supported, but it's not riskless.

The biggest threat is a prolonged bear market early in your coasting period. If you hit your Coast FIRE number and stop contributing, then the market drops 40% over the next two years, your portfolio needs to recover that loss and still grow to your target—all without any new contributions to help.

This is sequence of returns risk applied to accumulation rather than withdrawal. In traditional retirement planning, bad early returns devastate a portfolio that's being drawn down. In Coast FIRE, bad early returns devastate a portfolio that's no longer being built up.

A few ways to mitigate this:

• Add a margin of safety. Aim for 10–20% above your calculated Coast FIRE number before you stop contributing.
• Use conservative return assumptions. If you calculate with 5% real instead of 7%, you're building in a buffer against underperformance.
• Don't stop contributing entirely. Even small, irregular contributions during your coasting years meaningfully reduce risk.
• Run a simulation, not just a formula. A Monte Carlo simulation shows you the probability distribution of outcomes, not just the single “expected” case.

Calculate Your Coast FIRE Number

A static formula gives you a starting point, but your financial plan deserves better than a single number built on a single assumption. The FIREwiz accumulation calculator lets you enable Coast FIRE mode and run a full Monte Carlo simulation against historical market data. You'll see not just whether your number works in an average scenario, but how it holds up across the best and worst periods in market history.

Set your target FIRE number, your current portfolio, and your expected retirement age. The simulator will tell you whether you've already crossed the Coast FIRE threshold—and if not, how close you are. You can also track your portfolio balance over time with a free tool like Empower to see when you cross the line.