Coast FIRE Calculator

What Coast FIRE actually means (and why people love it)

Most retirement planning focuses on one question: how much do you need to save in total? Coast FIRE flips that. It asks: how much do you need invested right now so that you never have to add another dollar, and compound growth alone gets you to your retirement target?

Say you're 30 and want to retire at 65 with $50,000 a year in spending money. Using a 4% safe withdrawal rate, your full retirement number is $1.25 million. Sounds like a lot. But if your investments earn around 7% per year and inflation runs at 3%, your money roughly doubles in real terms every 18 years. That means you only need about $370,000 today. If you already have that much invested, you've reached Coast FIRE. You could switch to a lower-paying job you enjoy more, stop stressing about maxing out your 401(k), or simply enjoy the peace of mind that comes from knowing retirement is handled.

That's the appeal. You still work, but purely to cover your current living expenses. The pressure to save aggressively every single month goes away. For a lot of people, that mental shift is huge.

How the math works

The calculation has two steps. First, you figure out your full FIRE number: the total portfolio you need at retirement to live off withdrawals. The standard approach is to take your expected annual expenses in retirement and divide by your safe withdrawal rate. If you plan to spend $50,000 a year and use a 4% withdrawal rate, your FIRE number is $1,250,000.

Second, you discount that number back to today. This is just compound interest in reverse. Instead of asking "what will $X grow to in 35 years," you ask "what amount today will grow to $1.25 million in 35 years?" The formula is: Coast FIRE Number = FIRE Number divided by (1 + real return rate) raised to the power of years until retirement. The "real return rate" means your investment return minus inflation, because you want your answer in today's dollars, not inflated future dollars.

This calculator handles both steps for you. It also tracks your progress over time and tells you the exact age at which your current savings plus ongoing contributions will cross the Coast FIRE threshold.

Coast FIRE vs. regular FIRE vs. Barista FIRE

Regular FIRE means you have enough money to stop working entirely and live off your investments starting now. That's the big, ambitious target. Coast FIRE is much more reachable because you keep working to cover today's bills. You just don't need to save anymore. Your existing investments grow on autopilot to meet your future needs.

Barista FIRE is somewhere in between. With Barista FIRE, you have enough invested that you can switch to part-time or lower-paid work and supplement your living expenses with small portfolio withdrawals. Some people aim for Barista FIRE specifically to get health insurance through an employer while working fewer hours. Coast FIRE is more conservative: you don't touch the portfolio at all until your planned retirement age.

Why the return rate matters so much

Small changes in your assumed investment return create big differences in your Coast FIRE number. That's because compounding amplifies every fraction of a percent over decades. A 30-year-old assuming 7% returns and 3% inflation (so 4% real) might need $370,000 to coast. Change the return to 6% (3% real) and the number jumps to about $470,000. At 8% nominal (5% real), it drops to about $290,000.

This is why the calculator includes a sensitivity table showing your Coast FIRE number at different return rates. Nobody knows what the market will do over the next 30 years. Running multiple scenarios gives you a realistic range instead of a single number that might be too optimistic. If your current savings exceeds the Coast FIRE number even at a conservative 5% return, you can feel pretty confident about your position.

The role of inflation

Inflation is easy to ignore in a calculator, but over 30 or 40 years it changes everything. At 3% annual inflation, something that costs $50,000 today will cost about $121,000 in 30 years. If you project your retirement needs without accounting for inflation, you'll think you need less than you actually do.

This calculator adjusts for inflation by default. It uses your "real" return rate (nominal return minus inflation) so that every number it shows you is in today's purchasing power. When it says you need $370,000, that's $370,000 in today's dollars. You can toggle inflation off if you want to see nominal projections, but the inflation-adjusted view is more useful for actual planning.

What this calculator doesn't account for

This is a planning tool, not a crystal ball. It assumes your investments earn a steady rate every year, which isn't how markets work. Real returns bounce around. Some years you'll earn 20%, other years you'll lose 15%. The long-term average might be close to your assumption, but the path getting there will be bumpy.

It also doesn't factor in taxes. Money in a Roth IRA grows tax-free, but money in a traditional 401(k) gets taxed when you withdraw it. The calculator treats all savings equally. It also ignores Social Security, pensions, and any other income sources you might have in retirement. And it doesn't account for healthcare costs, which tend to rise faster than general inflation.

None of this means the calculator is useless. It gives you a solid directional answer: roughly how much do you need today, and are you on track? For most people, that's the right starting point. Just don't treat any single number as a guarantee.

How to get the most out of this tool

Start with honest numbers. Use your actual retirement savings balance (add up everything across all accounts), your real monthly contribution, and a realistic estimate of what you'd spend per year in retirement. For returns, 7% nominal is a reasonable starting point for a stock-heavy portfolio, though more conservative investors might want to use 6%.

After you run it once, change the inputs. Try a lower return rate to stress-test your plan. See what happens if you bump your retirement expenses up by $10,000. Check how much sooner you hit Coast FIRE if you increase your monthly contribution by $200. These experiments are where the real insight is. You start to see which variables actually move the needle and which ones barely matter.

The year-by-year table is especially useful for seeing the tipping point. You can watch your balance with contributions gradually catch up to (and then overtake) the Coast FIRE target for each year. Once those lines cross, you're coasting. Everything after that is bonus.

Related tools: Retirement Calculator, Compound Interest Calculator, and Savings Goal Calculator.