Coast FIRE is the portfolio size that compounds, without any further contributions, to your full FIRE number by traditional retirement age. After hitting Coast FIRE, you can stop saving and use future income for current lifestyle.
FIRE number
—
Coast FIRE number
—
Years to FIRE
—
Age at FIRE
—
Year-by-year projection
| Year | Age | Portfolio |
|---|
The moment you can stop feeding the account
Most retirement math asks how much you must keep saving. Coast FIRE flips the question. It asks how small a portfolio you need today so that, with zero further contributions, ordinary compound growth carries it to your full retirement target by the age you plan to stop working. Once you hit that threshold, every dollar you would have saved is freed up. You can downshift to a lower-paying job you actually enjoy, cover today's life with today's income, and let the existing balance ride.
The engine here computes two anchors. First it finds your FIRE number, the nest egg that funds your spending at a safe withdrawal rate. Then it discounts that figure back to the present at your expected real return, which gives the Coast FIRE number: the amount that, left alone, grows into the FIRE number by your target age. The gap between where you are and that threshold is the only saving you still owe.
Coasting from age 32 to 65
Walk the defaults. Annual expenses are $60,000 and the safe withdrawal rate is 4 percent, so the FIRE number is $60,000 divided by 0.04, which is $1,500,000. You are 32 and aiming to retire at 65, a 33-year runway, and you expect a 5 percent real return after inflation. To find the Coast FIRE number, discount $1,500,000 back 33 years: divide by 1.05 raised to the 33rd power, roughly 5.003. That comes to about $299,809. In plain terms, if you had close to $300,000 invested today and never added another cent, a 5 percent real return would compound it to about $1.5 million by 65. After that point, saving becomes optional rather than mandatory.
| Step | Result |
|---|---|
| Annual expenses | $60,000 |
| Safe withdrawal rate | 4 percent |
| FIRE number, $60,000 divided by 0.04 | $1,500,000 |
| Years to retirement, 65 less 32 | 33 years |
| Growth factor, 1.05 to the 33rd power | About 5.003 |
| Coast FIRE number, $1,500,000 divided by 5.003 | About $299,809 |
How $299,809 becomes $1.5 million
The curve below tracks the Coast FIRE balance compounding untouched from age 32 to 65 at a 5 percent real return. It starts near $300,000 and accelerates, because compound growth piles gains on prior gains. The teal point marks the starting threshold, and the line lands on the $1.5 million FIRE number right at age 65 with no contributions along the way.
Who Coast FIRE fits, and the assumption that can sink it
Coast FIRE suits people who saved aggressively early, often in their twenties and early thirties, and now want optionality rather than an even bigger pile. It is also a sanity check for younger savers wondering whether front-loading retirement accounts buys them freedom later. A practical tip: the single most sensitive input is the expected real return. The example uses 5 percent real, which is a reasonable long-run stock estimate after inflation, but drop it to 4 percent and the Coast FIRE threshold jumps meaningfully, because you are dividing by a smaller growth factor. Run the number at a conservative return so a disappointing decade does not blow up the plan.
Two cautions worth internalizing. First, reaching Coast FIRE does not mean you can stop earning. You still need income to cover current living expenses until retirement; you have only relieved yourself of further retirement saving. Second, this model assumes a steady real return, while real markets deliver lumpy, sometimes negative years. Sequence risk early in the coast can leave you behind the curve, so revisit the calculation every year or two and resume contributing if your balance drifts below the rising threshold. On the tax side, where your money sits matters: balances in a Roth grow and come out tax-free in retirement, while traditional 401(k) and IRA dollars are taxed on withdrawal, which effectively shrinks the spendable size of your FIRE number.
Should I use a real or a nominal return for this?
Use a real return, meaning the return after subtracting inflation, because the calculator already states your expenses and FIRE number in today's dollars. If you plugged in a nominal return such as 8 percent, you would understate the threshold badly, since part of that 8 percent is just inflation that also raises your future expenses. A 5 percent real assumption roughly corresponds to 8 percent nominal at 3 percent inflation.
Is Coast FIRE the same as being able to retire now?
No, and conflating the two is the most common misunderstanding. Coast FIRE means your existing investments will grow into a full retirement nest egg by your target age without more saving. You still need a paycheck to cover today's bills until then. Being able to retire now is full FIRE, where the portfolio is already large enough to live on.
What happens to my Coast FIRE number if I retire earlier?
An earlier target age shortens the compounding window, so the growth factor is smaller and the Coast FIRE threshold rises sharply. Retiring at 55 instead of 65 removes ten years of compounding, which can raise the amount you need today by a large margin. The later you let the money compound, the less you need to have accumulated to coast.