What is Coast FIRE?

Coast FIRE (also called Coast FI) is a milestone in the Financial Independence, Retire Early (FIRE) movement where you’ve saved enough that your investments will grow to support retirement on their own, without any additional contributions. Once you hit your Coast FIRE number, you still work to cover day-to-day expenses, but the pressure to save for retirement is gone.

If compound growth is doing the work, you don’t have to. That frees you to take a lower-paying job, cut back to part-time, switch careers, or simply stop stressing about your savings rate.

How Coast FIRE Works

The math behind Coast FIRE is compound growth. If you invest enough money early enough, time and market returns do the rest. A 30-year-old with $350,000 invested doesn’t need to add another dollar if they’re comfortable retiring at 60, because three decades of growth should carry that balance to a standard retirement target.

This is different from traditional FIRE, where the goal is to accumulate your full retirement number as fast as possible and stop working entirely. Coast FIRE splits the problem in two: save hard for a shorter window, then shift to covering only your current expenses for as long as you want to keep working.

The tradeoff is time. Coast FIRE only works if you have enough years between now and your target retirement age for compounding to close the gap. The younger you are when you reach it, the more powerful the effect.

Coast FIRE Formula and How to Calculate Your Number

Your Coast FIRE number is the amount you need invested today so that compound growth alone reaches your retirement target. The formula:

Coast FIRE Number = Retirement Target / (1 + r)^n

Where:

• Retirement Target = your annual retirement spending x 25 (the 4% rule)
• r = expected annual real return (after inflation, typically 5-7%)
• n = years until your target retirement age

Say you want $60,000 per year in retirement, you’re 30, and you plan to retire at 60. Your retirement target is $1,500,000 ($60,000 x 25). Assuming a 5% real return:

Coast FIRE Number = $1,500,000 / (1.05)^30 = roughly $347,000

If you have $347,000 invested at 30, you can stop contributing to retirement accounts entirely and still hit $1.5 million by 60, assuming 5% real returns.

Coast FIRE Number by Age

Your Coast FIRE number depends heavily on how many years of growth you have left. The younger you are, the less you need, because compounding has more time to work.

This table assumes $60,000 in annual retirement spending (a $1.5M target at 4%), 5% real returns, and retirement at 60:

The numbers shift significantly with different return assumptions. At 7% real returns, a 30-year-old’s Coast FIRE number drops to about $197,000. At 4%, it rises to $463,000. Your assumed rate of return is the single most sensitive variable in the calculation, which is why stress-testing it matters more than getting a precise number.

A Coast FIRE calculator like ProjectionLab lets you plug in your actual portfolio, adjust return assumptions, and factor in Social Security, pensions, and other income sources that a simple formula can’t capture.

Coast FIRE vs. Barista FIRE

These are the two most commonly confused FIRE strategies. Both involve continued work, but the relationship to your portfolio is different.

With Coast FIRE, you’ve saved enough that your investments will grow to your retirement number on their own. You’re not touching your portfolio. You work to cover current expenses only.

With Barista FIRE, you’ve saved enough that part-time income plus portfolio withdrawals cover your expenses. You’re actively drawing down your portfolio now.

Many people hit Coast FIRE first on their way to Barista FIRE or full FIRE. Reaching Coast FIRE doesn’t mean you stop saving; it means you no longer have to.

Risks and Limitations

Coast FIRE depends on assumptions about future returns, and those assumptions carry real uncertainty.

Sequence of returns in the growth phase. The formula assumes a smooth average return, but real markets don’t work that way. A prolonged downturn early in your coasting period can significantly delay when your portfolio reaches its target. Running Monte Carlo simulations rather than relying on a single average return gives a more honest picture of your range of outcomes.

Inflation surprises. The formula uses real (inflation-adjusted) returns, but actual inflation can deviate from historical norms for extended periods. If inflation runs higher than expected, your retirement target in nominal dollars grows faster than your portfolio.

Lifestyle changes. Your $60,000 spending assumption at 30 may not hold at 50. Kids, healthcare costs, housing decisions, and lifestyle inflation can all push your actual retirement target higher than what you planned for.

Frequently Asked Questions

How much do I need for Coast FIRE? A 30-year-old targeting $60,000/year at age 60 needs roughly $347,000 at 5% real returns. The number shifts with your age, target retirement date, expected returns, and spending level. Use the formula (Retirement Target / (1 + r)^n) or a calculator that can factor in your full financial picture.

Should I stop saving after reaching Coast FIRE? You can, but most people don’t entirely. Any additional savings accelerate your timeline toward full FIRE or give you a cushion against worse-than-expected returns. Coast FIRE is a milestone that removes the obligation to save, not necessarily the desire.

What’s the difference between Coast FIRE and regular FIRE? Regular FIRE means you have enough to stop working and live off investments now. Coast FIRE means your current savings will grow to that amount by a future date, but you still need income to cover today’s expenses.

What happens if the market crashes after I reach Coast FIRE? You have time on your side. If you’re 35 and targeting retirement at 60, that’s 25 years for your portfolio to recover from a downturn. You can also resume contributions temporarily to get back on track. The bigger risk is a prolonged period of low returns rather than a single crash.

Can I calculate Coast FIRE as a couple? Yes, but it’s more complex. You need to account for two sets of retirement spending, two Social Security timelines, and potentially different retirement ages. A planning tool that supports couples will give you a more accurate picture than running the formula twice.