What Is a Coast FIRE Number and How Do You Calculate Yours?
Your Coast FIRE number is the amount you need invested today so compound growth carries you to full retirement — without another dollar of contributions. Here's the formula and worked examples.
What Is a Coast FIRE Number?
Your Coast FIRE number is the amount of money you need invested right now — at your current age — such that, even if you never contribute another dollar, your portfolio will grow to your full retirement target by the time you reach traditional retirement age.
Once you hit it, you've removed the retirement savings pressure from your financial life. You still need to earn enough to cover day-to-day expenses. But you no longer need to save for the future — the future is already funded. Your investments are "coasting" to the finish line.
It's a different kind of milestone than full FIRE. It doesn't mean you can stop working entirely. But it means the retirement question is essentially answered, which changes your relationship to your career and financial decisions in meaningful ways.
For a deeper understanding of how Coast FIRE fits into the broader landscape of FIRE approaches, see our Coast FIRE explainer.
The Math Behind It
Coast FIRE uses the future value of money formula, rearranged to solve for the present value you need today.
The future value formula:
FV = PV × (1 + r)^n
Where:
- FV = Future value (your full FIRE number at retirement)
- PV = Present value (what you need invested today — your Coast FIRE number)
- r = Annual return rate (as a decimal)
- n = Years until retirement
Rearranging to solve for the present value (your Coast FIRE number):
Coast FIRE Number = FIRE Number ÷ (1 + r)^n
This formula answers: how much money, invested today at a given return rate, will compound to your target FIRE number in n years?
A Worked Example
Setup:
- Current age: 32
- Target retirement age: 65
- Planned annual retirement expenses: $55,000
- Full FIRE number: $55,000 × 25 = $1,375,000
- Expected annual return: 7% (a reasonable inflation-adjusted long-term estimate for a diversified stock portfolio)
- Years to retirement: 33
Coast FIRE Number = $1,375,000 ÷ (1.07)^33
First, calculate (1.07)^33 = approximately 9.32
Coast FIRE Number = $1,375,000 ÷ 9.32 = $147,600
At 32, if you have $147,600 invested in index funds and never contribute another dollar, you will have approximately $1,375,000 at age 65 at a 7% average return.
That's the power of time and compounding. $147,600 today does the work of nearly a million dollars over three decades.
Use our Coast FIRE Calculator to calculate your exact number — no manual math required.
Coast FIRE Numbers by Age and Target
The table below shows Coast FIRE numbers at different ages, assuming a 7% annual return and a target retirement age of 65.
| Current Age | Years to 65 | FIRE Target $1M | FIRE Target $1.5M | FIRE Target $2M |
|---|---|---|---|---|
| 25 | 40 | $67,300 | $100,900 | $134,600 |
| 30 | 35 | $94,600 | $141,900 | $189,200 |
| 35 | 30 | $131,400 | $197,200 | $262,900 |
| 40 | 25 | $184,200 | $276,300 | $368,400 |
| 45 | 20 | $258,400 | $387,600 | $516,800 |
| 50 | 15 | $362,400 | $543,600 | $724,700 |
A few things stand out from this table:
Starting early has an outsized impact. A 25-year-old with a $1.5M target needs only $100,900 in Coast FIRE savings. A 40-year-old with the same target needs nearly $276,000 — almost three times as much. Every year you wait costs you in compound growth.
The jump from 25 to 35 is steep. Between age 25 and 35, the required Coast FIRE number roughly doubles. The decade from 25 to 35 is the highest-leverage decade for reaching Coast FIRE.
A lower target retirement age raises your Coast number. The table uses 65 as the target. If you want to retire at 55, your n drops from, say, 30 years (at age 35) to 20 years — which means the denominator in the formula is smaller, and your Coast FIRE number is higher.
What to Do After Reaching Your Coast FIRE Number
Reaching your Coast FIRE number doesn't require any single dramatic action. But it does create options:
Option 1: Stay the course
Keep saving and investing as before. You'll reach full FIRE faster and with a larger portfolio. Coast FIRE is a floor, not a ceiling.
Option 2: Reduce work hours
If you only need to cover current living expenses (not save for the future), a lower-income job might suffice. Many people shift to part-time, freelance, or lower-stress work once they hit Coast FIRE. Read about Barista FIRE for a similar approach.
Option 3: Change careers
High-stress careers often demand high salaries. Once you've hit Coast FIRE, you can afford to pursue lower-paying work that's more meaningful, less demanding, or better aligned with your values — because you've already funded retirement.
Option 4: Take extended time off
A sabbatical, extended travel, or time raising young children becomes more viable when you're not worried about setting back your retirement savings. Your existing portfolio keeps compounding while you're away from the workforce.
Important Assumptions to Revisit
The Coast FIRE formula depends heavily on three inputs:
The return rate assumption: 7% is a commonly used real (inflation-adjusted) long-term return for a diversified stock portfolio, based on historical U.S. market performance. The actual number could be meaningfully higher or lower. Some planners use 6% for more conservative projections. If you use 5% instead of 7% in the example above, your Coast FIRE number increases substantially.
The retirement age assumption: Coast FIRE only works as described if you actually let the money grow undisturbed until your target retirement date. Withdrawing early, even for emergencies, disrupts the calculation.
The FIRE number assumption: Your Coast FIRE number is derived from your full FIRE number, which is based on your projected retirement expenses. If your lifestyle changes significantly, your Coast number needs to be recalculated.
This is why the calculator matters: small changes in assumptions produce large changes in the output. Run multiple scenarios with different return rates and target retirement ages to understand the range you're working within, not just a single number.
This article is for educational purposes only and does not constitute financial or investment advice. Investment returns are not guaranteed and will vary. Consult a qualified financial professional for guidance specific to your situation.
Topics
Frequently asked.
§ FAQ01What is a Coast FIRE number?
What is a Coast FIRE number?
A Coast FIRE number is the amount of money you need invested today so that compound growth alone — with no additional contributions — will grow your portfolio to your full retirement target by traditional retirement age. Once you hit it, you only need to earn enough to cover current living expenses; your retirement is mathematically already funded.
02How do you calculate your Coast FIRE number?
How do you calculate your Coast FIRE number?
Use the present value formula: Coast FIRE number = FIRE number ÷ (1 + r)^n, where r is your expected real annual investment return and n is the number of years until you want to reach full FIRE. Example — a $1,500,000 FIRE number, 35 years of compounding, and a 7% real return gives a Coast number of roughly $140,000.
03What return rate should I use?
What return rate should I use?
Most FIRE planners use 7% real (inflation-adjusted) returns, matching the long-run average of a diversified U.S. stock portfolio. Conservative planners use 5-6% to account for lower expected future returns. Always use real (inflation-adjusted) rates in Coast FIRE math — mixing nominal and real returns is the most common error.
04At what age should you aim to hit Coast FIRE?
At what age should you aim to hit Coast FIRE?
There's no single right answer, but community data suggests the most common targets are 30, 35, and 40. The earlier you hit Coast FIRE, the lower the required dollar amount — because you have more years for compounding. Hitting Coast FIRE at 30 instead of 40 can cut the required amount by 40-50%.
05Can you Coast FIRE with a Roth IRA?
Can you Coast FIRE with a Roth IRA?
Yes. Roth IRAs are one of the best vehicles for Coast FIRE because all growth is tax-free in retirement — you don't need to plan for future tax rates on withdrawals. The contribution limit is the main constraint ($7,000-$8,000 per year as of 2026), so most Coast FIRE plans combine Roth IRA with a 401(k) or taxable brokerage account.
06Is Coast FIRE the same as 'set it and forget it' investing?
Is Coast FIRE the same as 'set it and forget it' investing?
In terms of contributions, yes — after hitting the Coast number you can stop adding to retirement accounts. But the investments themselves still require ongoing management: periodic rebalancing, monitoring expense ratios, adjusting allocation as you approach retirement age. Coast FIRE removes the savings pressure, not the stewardship responsibility.
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This article is for educational purposes only and does not constitute financial, tax, or investment advice. All financial decisions involve risk. Past performance is not indicative of future results. Please consult a qualified financial professional before making investment or retirement planning decisions. Read our full disclaimer.
More from the archive.
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