Calculating your Coast FIRE number is simpler than you might think. With just three numbers—your retirement goal, years until retirement, and expected investment return—you can determine if you’re already financially free to stop saving for retirement.

What is a Coast FIRE Number?

Your Coast FIRE number is the amount of money you need saved today so that compound interest alone (with zero additional contributions) will grow it to your retirement goal by your target retirement age.

Think of it as your “point of no return” for retirement savings. Once you hit this number, you can coast to retirement without contributing another dollar.

The Coast FIRE Formula

Coast FIRE Number = Retirement Goal ÷ (1 + Return Rate)^Years

Where:

• Retirement Goal = Total amount needed at retirement
• Return Rate = Expected annual investment return (as a decimal)
• Years = Time until retirement age

Step-by-Step Calculation

Step 1: Determine Your Retirement Goal

Use the 4% rule as a starting point. Multiply your desired annual retirement spending by 25.

Example:

• Desired annual spending: $70,000
• Retirement goal: $70,000 × 25 = $1,750,000

The 4% rule suggests you can safely withdraw 4% of your portfolio annually in retirement without running out of money.

Step 2: Calculate Years Until Retirement

Subtract your current age from your target retirement age.

Example:

• Current age: 35
• Target retirement age: 65
• Years until retirement: 65 - 35 = 30 years

Step 3: Choose an Expected Return Rate

Be conservative here. Historical stock market returns average 10%, but financial planners typically use 7-8% after inflation.

For Coast FIRE, we recommend using 7% (0.07 as a decimal) for safety.

Step 4: Apply the Formula

Let’s calculate with our example numbers:

Coast FIRE Number = $1,750,000 ÷ (1.07)^30
                  = $1,750,000 ÷ 7.612
                  = $229,900

Result: If you have $229,900 saved at age 35, you can stop contributing and it will grow to $1.75 million by age 65 (assuming 7% returns).

Real Examples

Example 1: Young Professional

Profile:

• Age: 28
• Current savings: $75,000
• Retirement goal: $2,000,000
• Years until 65: 37 years

Calculation:

$2,000,000 ÷ (1.07)^37 = $2,000,000 ÷ 11.42 = $175,000

Status: Needs $100,000 more to reach Coast FIRE

At their current savings rate of $2,000/month, they’ll hit Coast FIRE in about 3 years (age 31). After that, they can reduce or eliminate retirement contributions.

Example 2: Mid-Career Professional

Profile:

• Age: 42
• Current savings: $350,000
• Retirement goal: $1,500,000
• Years until 65: 23 years

Calculation:

$1,500,000 ÷ (1.07)^23 = $1,500,000 ÷ 4.74 = $316,000

Status: Already coasting! ($350,000 > $316,000)

This person has been a diligent saver and is already past their Coast FIRE number. They can stop contributing to retirement accounts and still reach their goal.

Example 3: Late Starter

Profile:

• Age: 45
• Current savings: $120,000
• Retirement goal: $1,200,000
• Years until 65: 20 years

Calculation:

$1,200,000 ÷ (1.07)^20 = $1,200,000 ÷ 3.87 = $310,000

Status: Needs $190,000 more

This person needs to continue aggressive saving. At $3,000/month, they’ll reach Coast FIRE in about 5 years (age 50).

Using Different Return Assumptions

Your Coast FIRE number changes dramatically based on return assumptions. Here’s how a $2M retirement goal at age 35 (30 years out) varies:

Return Rate	Coast FIRE Number	Difference
6%	$348,000	Most conservative
7%	$262,000	Recommended
8%	$198,000	Optimistic
9%	$150,000	Aggressive
10%	$114,000	Very aggressive

Our recommendation: Use 7% for planning. If markets outperform, you’ll reach your goal earlier or have a larger nest egg.

The Impact of Time

Time is the most powerful variable in the Coast FIRE formula. The earlier you start, the less you need.

$2 million retirement goal at 7% returns:

Current Age	Years to 65	Coast FIRE Number
25	40 years	$134,000
30	35 years	$188,000
35	30 years	$262,000
40	25 years	$366,000
45	20 years	$517,000
50	15 years	$725,000

Notice how the Coast FIRE number nearly doubles every 5 years you delay. Time is your biggest asset.

Adjusting for Different Retirement Ages

Want to retire earlier than 65? Your Coast FIRE number increases because there’s less time for compound growth.

For a 35-year-old with a $2M goal:

Target Retirement Age	Years	Coast FIRE Number
55	20 years	$517,000
60	25 years	$366,000
65	30 years	$262,000
70	35 years	$188,000

Each year you delay retirement reduces your Coast FIRE number by roughly 7% (at 7% returns).

Common Mistakes to Avoid

1. Using Too Aggressive Return Assumptions

Using 10%+ returns makes your Coast FIRE number look achievable, but market volatility could leave you short. Stick with 7-8%.

2. Forgetting About Inflation

The retirement goal should be in today’s dollars, and your return rate should be real returns (after inflation). Most calculators handle this automatically.

3. Not Including a Safety Margin

Calculate your Coast FIRE number, then add 10-20% as a buffer for market volatility and unexpected life changes.

4. Ignoring Taxes

If your retirement savings are in traditional 401(k)/IRA accounts, you’ll pay taxes on withdrawals. Your real retirement goal might be 20-30% higher than you think.

Beyond the Basic Formula

Account for Social Security

If you’ll receive Social Security, you can reduce your retirement goal. For example:

• Original goal: $2,000,000 ($80,000/year × 25)
• Expected Social Security: $30,000/year
• Adjusted goal: $1,250,000 ($50,000/year × 25)

This significantly reduces your Coast FIRE number.

Consider Pension Income

Similar to Social Security, any pension income reduces the amount you need to fund yourself.

Factor in Part-Time Work

Planning to do some part-time work in retirement? Reduce your retirement goal accordingly.

Use a Calculator Instead

While the math isn’t complex, a calculator handles all the details and lets you test different scenarios instantly.

Calculate Your Coast FIRE Number →

Our calculator lets you:

• Adjust return rate assumptions (5-10%)
• Test different retirement ages
• See year-by-year growth projections
• Account for additional contributions
• Visualize your path to Coast FIRE

What to Do After Calculating

If You’ve Already Reached Coast FIRE:

1. Verify your numbers - Be conservative, add a safety margin
2. Decide your next move - Keep contributing? Reduce contributions? Stop entirely?
3. Make a career decision - Now’s the time for that lower-paying dream job
4. Maintain an emergency fund - 6-12 months of expenses outside retirement accounts

If You Haven’t Reached Coast FIRE Yet:

1. Calculate the gap - How much more do you need?
2. Project your timeline - At your current savings rate, when will you hit it?
3. Consider increasing contributions - Reaching Coast FIRE sooner gives you more freedom
4. Track quarterly - Market gains might get you there faster than you think

The Freedom of Knowing Your Number

Once you calculate your Coast FIRE number, you have clarity. You know exactly:

• How much is enough to stop saving for retirement
• Whether you’re on track or need to adjust
• When you can reduce your financial stress
• What career flexibility you can afford

This number represents financial peace of mind. You don’t need to reach full FIRE to gain significant freedom—Coast FIRE is an achievable milestone that changes how you think about work and money.

Calculate Yours Now

Stop guessing whether you’ve saved enough. In 2 minutes, you can know your exact Coast FIRE number and how close you are.

Use Our Free Calculator →

No email required. No signup. Just enter your numbers and get your answer.

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The Coast FIRE number is a planning tool, not a guarantee. Actual investment returns vary, and you should consult with a financial advisor before making major financial decisions.