What is Coast FIRE, exactly?

It's the point where your existing investments, left completely untouched, are projected to grow into a full retirement fund by your target age. After that point you only need to earn enough to cover current living costs — retirement saving itself is optionally done.

Why use a real (after-inflation) return?

Because your retirement spending is entered in today's dollars. Using an inflation-adjusted return keeps both sides of the equation in the same units, so the projection means what it appears to mean. A common approach is to subtract expected inflation from your nominal return assumption.

Is the 4% withdrawal rate safe?

It's a research-derived rule of thumb, not a guarantee — based on historical US market data over 30-year retirements. Longer retirements and more cautious assumptions argue for 3–3.5%. Try both in the calculator; the Coast number is quite sensitive to it.

I've hit my Coast number. Should I actually stop saving?

Reaching Coast FIRE means you could — it doesn't mean you must. The projection assumes decades of average returns that markets won't deliver smoothly. Many people keep saving at a relaxed pace and treat the milestone as what it really is: the point where work becomes more of a choice.

Coast FIRE Calculator — When Compounding Takes Over

Coast FIRE Calculator

Coast FIRE is the point where compounding takes over: invested assets that will grow into a full retirement without another dollar added. Find your number and your gap.

Current ageRetirement age

Annual spending in retirement$In today's dollars — the real-return assumption below handles inflation.Safe withdrawal rate%4% is the common rule-of-thumb starting point; more conservative planners use 3–3.5%.Currently invested$Expected real return (after inflation)%

Your Coast FIRE number: $181,290
Full FI number at retirement: $1,000,000
Still to invest: $131,290
Your current investments grow to: $275,801

Once your investments reach the Coast number, compounding alone is projected to carry you to retirement — every dollar saved before then counts double.

The milestone before the milestone

Full financial independence takes most people decades. Coast FIRE is the earlier, stranger milestone: the day your invested assets are projected to finish the job on their own. Every dollar invested young works longer than a dollar invested later — Coast FIRE is where those early dollars, compounded to your retirement age, cover the whole target.

The formula

FI number = annual retirement spending ÷ safe withdrawal rate
Coast number = FI number ÷ (1 + real return)^(years until retirement)
You've reached Coast FIRE when your invested assets ≥ your Coast number.

How to use the result

The gap to your Coast number is the most motivating figure in personal finance: it shrinks from both sides, as you save and as time passes. Knowing it changes decisions — how hard to push savings now, whether a lower-paying job you'd love is affordable, when downshifting becomes possible. Revisit yearly with updated balances and assumptions; it's a projection, not a promise.

A quick example

With the calculator's starting assumptions, $40,000 of annual retirement spending and a 4% withdrawal-rate assumption imply a $1,000,000 FI number. If you are 30, plan to retire at 65, and assume a 5% annual return after inflation, that target discounts to roughly $181,000 today. A current invested balance of $50,000 is therefore not yet at Coast FIRE, but it makes the gap concrete. Change the spending, age, return, and withdrawal assumptions one at a time to see which ones actually drive your result.

Why the assumptions matter more than the label

Coast FIRE works only if the future behaves close enough to the model. A real return keeps the investment projection in today's purchasing power, but actual returns arrive unevenly and inflation is not known in advance. A withdrawal rate is a planning assumption, not a promise of safe spending. Try a lower return and a lower withdrawal rate as a stress test; if the plan only works under one optimistic set of inputs, it is not yet a durable plan. Many people continue saving after reaching the number to leave room for uncertainty and changing goals.

What this calculator leaves out

The model does not include investment fees, taxes, pension income, Social Security, healthcare costs, changes in spending, or the risk of poor market returns early in retirement. It also does not recommend an asset allocation or tell you whether to stop saving. The U.S. SEC's Investor.gov compound-interest calculator is a useful companion for testing a range of return assumptions. WorthMath provides a general educational projection, not personalized investment, tax, or retirement advice.

Frequently asked questions

What is Coast FIRE, exactly?: It's the point where your existing investments, left completely untouched, are projected to grow into a full retirement fund by your target age. After that point you only need to earn enough to cover current living costs — retirement saving itself is optionally done.
Why use a real (after-inflation) return?: Because your retirement spending is entered in today's dollars. Using an inflation-adjusted return keeps both sides of the equation in the same units, so the projection means what it appears to mean. A common approach is to subtract expected inflation from your nominal return assumption.
Is the 4% withdrawal rate safe?: It's a research-derived rule of thumb, not a guarantee — based on historical US market data over 30-year retirements. Longer retirements and more cautious assumptions argue for 3–3.5%. Try both in the calculator; the Coast number is quite sensitive to it.
I've hit my Coast number. Should I actually stop saving?: Reaching Coast FIRE means you could — it doesn't mean you must. The projection assumes decades of average returns that markets won't deliver smoothly. Many people keep saving at a relaxed pace and treat the milestone as what it really is: the point where work becomes more of a choice.