Coast FIRE is the point where the retirement investments you already own are projected to grow to your future retirement target without requiring additional retirement contributions.
You have not necessarily retired when you reach Coast FIRE.
You may still work full time, reduce your hours, change jobs, run a business, or keep doing exactly what you were doing before. You still need a way to cover today's living expenses.
The difference is mathematical: under the assumptions in your projection, the money already invested has enough time to do the remaining retirement-saving work through compound growth.
That is the “coast” part.
The two phases of Coast FIRE
Coast FIRE separates retirement planning into two distinct phases:
Build phase
Contribute aggressively until your invested assets reach your personal Coast FIRE number.
Coast phase
Allow those investments to compound over time toward your full retirement target with $0 required new savings.
The number depends heavily on your retirement spending, retirement age, investment return, inflation treatment and withdrawal-rate assumption.
A Coast FIRE number without those assumptions is incomplete.
What does Coast FIRE actually mean?
The basic idea is easier to understand if you start with your future retirement target.
Suppose you want a portfolio of $1.5 million when you retire.
That distinction is the entire concept.
Compound growth matters because investment gains can themselves generate future gains.
The longer the time between today and retirement, the more important that compounding period becomes.
The three dates that matter in Coast FIRE
One reason Coast FIRE gets confusing is that people often treat several different ages as though they were the same.
They are not.
1. Your Coast FIRE age
This is the age when your existing investments first meet the calculated Coast target.
2. Your planned retirement age
This is when the model assumes your retirement portfolio needs to support retirement spending. It could be 50, 60, 65, 67 or another age.
3. Your benefit or account-access ages
Social Security, pensions, Medicare and retirement-account access can operate on their own timelines. For example, the Social Security Administration says full retirement age is 67 for people born in 1960 or later. It currently allows retirement benefits to begin as early as age 62, although the benefit is reduced when claimed that early. Those are Social Security rules. They do not define your Coast FIRE retirement age.
Coast at 38 → reduce work at 45 → retire at 60 → Social Security at 67
The dates answer different questions.
A Coast FIRE example
Consider this illustrative case.
| Input | Example |
|---|---|
| Current age | 35 |
| Planned retirement age | 65 |
| Years until retirement | 30 |
| Annual retirement spending | $60,000 |
| Withdrawal-rate assumption | 4% |
| Real-return assumption | 5% |
First, we need a modeled retirement target.
Using a 4% withdrawal-rate assumption:
So this example uses a retirement portfolio target of:
Now work backward.
How much money would need to be invested at age 35 for it to grow to $1.5 million by age 65 if it earns an average 5% real return over those 30 years?
The result is approximately:
Under these exact assumptions, about $347,000 today is mathematically projected to become $1.5 million over 30 years without additional contributions.
That does not mean $347,066 guarantees $1.5 million.
It means the projection reaches $1.5 million if the modeled assumptions occur.
Your Coast FIRE number can change a lot
The return assumption is a good example.
Keep the same:
- age;
- 30-year timeline;
- $1.5 million retirement target;
and change only the real return.
| Real return used | Approx. amount needed today |
|---|---|
| 3% | $617,980 |
| 4% | $462,478 |
| 5% (Example Baseline) | $347,066 |
| 6% | $261,165 |
| 7% | $197,051 |
That is a difference of more than $420,000 between the 3% and 7% assumptions.
So statements such as:
“You need $197,000 for Coast FIRE”
are not useful without context.
The real question is:
“$197,000 at what age, for what retirement target, using what return and for how many years?”
Is 7% the normal Coast FIRE return?
There is no government-approved or universally correct Coast FIRE return rate.
Historical market returns can help inform assumptions, but future returns are uncertain.
A 7% real return is also very different from a 7% nominal return.
Real return accounts for inflation.
Nominal return does not.
That distinction becomes important when a Coast calculation spans several decades.
A better calculator therefore lets users change the assumption and see how sensitive the result is rather than presenting one percentage as fact.
What does the 4% rule have to do with Coast FIRE?
The 4% rule is often used to estimate the full retirement portfolio before calculating today's Coast FIRE number.
It is not the definition of Coast FIRE.
The historical research behind the commonly cited withdrawal-rate concept includes William Bengen's 1994 “Determining Withdrawal Rates Using Historical Data” and later work by Cooley, Hubbard and Walz examining withdrawal sustainability across historical stock-and-bond portfolios.
Importantly, the Cooley, Hubbard and Walz article itself notes that no single withdrawal rate appears appropriate for every investor and frames withdrawal rates as planning choices under uncertainty rather than guaranteed outcomes.
For Coast FIRE, the withdrawal-rate assumption matters because it determines the eventual retirement portfolio target.
For $60,000 of annual retirement spending:
- 3% implies a $2,000,000 target;
- 4% implies a $1,500,000 target;
- 5% implies a $1,200,000 target.
Different target → different Coast FIRE number.
Reaching Coast FIRE does not mean retiring today
This is probably the biggest misunderstanding around Coast FIRE.
Imagine you are 40 and your calculator says your investments have reached the Coast number for retirement at age 65.
It does not mean those investments can necessarily support all your expenses from age 40 onward.
You still have 25 years of:
- • housing;
- • food;
- • utilities;
- • healthcare;
- • transportation;
- • taxes;
- • family costs;
- • travel;
- • and everything else in your current budget.
Those expenses still require funding.
That is the main difference between Coast FIRE and full FIRE.
| Comparison Metric | Coast FIRE | Full FIRE |
|---|---|---|
| Portfolio expected to fund expenses immediately | Usually no | Generally yes |
| Work income may still be needed | Yes | Not required by the basic model |
| New retirement contributions required by projection | No | No |
| Portfolio phase | Usually accumulating | Often withdrawing |
| Main question | Can today's portfolio grow to the future target? | Can today's resources support retirement now? |
Do people really stop investing after reaching Coast FIRE?
Not always. And they do not have to.
Reaching Coast FIRE simply means zero future retirement contributions work in the selected mathematical scenario.
A separate scenario can still contain future contributions.
This distinction shows up in current Coast FIRE discussions.
The $0-contribution setting is a model condition used to isolate compound growth. It does not require someone to stop investing, and a separate contribution scenario can be compared with the zero-contribution result.
An August 2026 discussion similarly asked what people actually did with money that had previously gone toward retirement savings after reaching their Coast number.
Those are individual experiences, not financial rules.
They illustrate why a calculator should distinguish between:
$0 future contributions
User-selected future contributions
The user can compare the math without the calculator deciding which path is preferable.
Inflation can materially change a Coast FIRE projection
Long Coast FIRE timelines make inflation particularly important.
The latest available U.S. CPI data at the time of this review show that consumer prices were 3.4% higher in July 2026 than one year earlier. Prices excluding food and energy were up 2.5% over the same period.
That does not mean a calculator should assume 3.4% inflation every year for the next 30 years.
The important thing is consistency.
A model can work in:
today's dollars + real returns
future dollars + nominal returns
How much retirement spending should you use?
There is no official Coast FIRE spending target.
Your retirement-spending estimate has a major effect on the result because spending determines the portfolio you are trying to reach.
For real-world context, the Bureau of Labor Statistics reported that the average U.S. consumer unit spent $78,535 in 2024, or about $6,545 per month.
That average included:
- $26,266 on housing, or 33.4% of expenditures;
- $13,318 on transportation, or 17.0%.
Together, those two categories accounted for just over half of average expenditures.
Someone entering retirement might:
- • have no mortgage;
- • still rent;
- • move;
- • travel more;
- • drive less;
- • support family members;
- • face different healthcare costs.
The calculator should therefore use the spending estimate the user actually wants to model rather than substituting a nationwide average.
Why younger Coast FIRE numbers can look surprisingly low
Time has a huge effect.
If two people both want $1.5 million at retirement, but one has 30 years for the portfolio to grow while the other has only 10, they will not have the same Coast FIRE number today.
The younger investor's target may look surprisingly small because more of the future target is being assigned to compound growth.
That is mathematics—not a guarantee that markets will deliver the assumed return.
It is also why a Coast FIRE number should never be presented without:
What can change your Coast FIRE number?
Your Coast FIRE number is not permanent.
It can change when any important input changes.
Retirement spending changes
Higher modeled spending usually means a larger retirement portfolio target.
Retirement age changes
More time generally means more opportunity for compounding. Less time means less.
Return assumptions change
As the earlier table showed, even a few percentage points can materially change today's required amount.
Withdrawal-rate assumptions change
A lower withdrawal rate generally creates a larger full-retirement target.
Inflation treatment changes
Real and nominal calculations must be handled consistently.
Fees change
Investment costs reduce net returns and can affect a long compounding period.
Pension or Social Security estimates change
Future recurring income may reduce the amount of retirement spending the investment portfolio must fund after those benefits begin.
Money is withdrawn from the retirement portfolio
Taking assets out means less capital remains available to compound.
That is why Coast FIRE is better treated as a calculation to review periodically rather than a permanent certification.
Coast FIRE is a projection, not a promise
A Coast FIRE calculator simplifies decades of uncertainty into a set of assumptions.
It cannot know:
- • future market returns;
- • future inflation;
- • future tax law;
- • exactly how much you will spend;
- • exactly when you will retire;
- • whether pension benefits will change;
- • future healthcare costs;
- • or whether you will withdraw money before retirement.
That does not make the calculation useless.
It means the assumptions should be visible.
A useful Coast FIRE result should tell you not only:
“Your Coast FIRE number is $X”
but also:
“This result assumes X% return, Y% inflation treatment, Z% withdrawal rate and N years until retirement.”
That makes the calculation auditable rather than mysterious.
Frequently Asked Questions
What does Coast FIRE mean?
Coast FIRE means your current retirement investments are projected to grow to your future retirement target without additional retirement contributions, based on the assumptions used in the calculation.
Is Coast FIRE the same as retirement?
No. Coast FIRE generally assumes current living expenses still need to be funded until the modeled retirement date. Full retirement requires a separate assessment of whether current resources can support current spending.
Do I have to stop contributing after reaching Coast FIRE?
No. Zero future contributions define the Coast projection, but you can separately model continued contributions. Reaching Coast FIRE does not require changing an existing retirement contribution.
Can my Coast FIRE number increase after I have reached it?
Yes. A change in retirement spending, retirement age, return assumptions, withdrawal rate, fees, inflation treatment or future benefit estimates can change the number.
Is 7% the correct return rate for Coast FIRE?
There is no single universally correct return rate. In the example above, using a 3% real return produces a Coast target of roughly $618,000 while a 7% real return produces about $197,000 for the same $1.5 million target and 30-year period.
Does Social Security count toward Coast FIRE?
It can be modeled as future retirement income when an estimated benefit and start age are supplied. It should not automatically be counted as part of the current investment portfolio.
Does home equity count toward Coast FIRE?
Not automatically. A basic Coast FIRE calculation generally focuses on assets intended to fund retirement. Home equity would need an explicit assumption about how and when it becomes available for retirement spending.
The bottom line
Coast FIRE is not a magic age or a universal dollar amount.
It is a relationship between:
When the first number is large enough that projected compound growth can reach the future target without additional contributions, you have reached the modeled Coast FIRE point.
The word modeled matters.
Your result depends on assumptions, and those assumptions can change.
That is why the most useful question is not:
“How much money do you need for Coast FIRE?”
It is:
“What is my Coast FIRE number using my spending, retirement date and assumptions?”
Calculate your Coast FIRE number
Enter your current age, investments, retirement spending, retirement age and assumptions to see:
- your modeled Coast FIRE target;
- current gap or surplus;
- projected retirement value;
- and the assumptions behind the result.
Verified Sources & Methodology
Compound Interest Calculator
Consumer Price Index (CPI)
Consumer Expenditures 2024
Retirement Claiming Ages (62–70)
Safe Withdrawal Rate Study
Trinity Study (AAII 1998)
Community Discussions
2026 Federal Brackets
What about Social Security?
Social Security can be incorporated into a more advanced Coast FIRE calculation, but it should be treated as future income beginning at a specified age—not as money already sitting in your investment account.
For people born in 1960 or later, SSA currently lists:
Those percentages describe Social Security benefit timing under current rules.
They are not Coast FIRE assumptions.
For personalized calculations, a user-entered SSA benefit estimate is more useful than a generic national benefit figure.