Coast FIRE Calculator: When Can You Stop Contributing?

Imagine reaching a point where your current investments will grow to your retirement goal without adding another dollar. That's Coast FIRE—the moment you can step off the contribution treadmill and let compound growth do the heavy lifting.

Most people think about FIRE as an all-or-nothing switch: either you're working and saving aggressively, or you've hit your number and retired completely. Coast FIRE is the third option—the sweet spot where you can shift gears to part-time work, lower-stress roles, or projects that actually excite you, knowing your retirement is already mathematically guaranteed.

Why Coast FIRE Matters

The financial freedom these numbers represent is profound:

Freedom to choose: Drop to part-time work without sacrificing your retirement timeline
Stress reduction: Remove the pressure of hitting a specific savings target each month
Life optimization: Take that sabbatical, pursue a passion project, or spend more time with family
Psychological win: You've already "won" at saving—now it's just waiting

The Math Behind Coast FIRE

Here's the beautiful simplicity: If you need $1 million to retire comfortably and your investments will grow to exactly $1 million by age 65 through compound growth alone, you can coast there today.

The calculation:

Current Investment Balance × (1 + Annual Return Rate)^Years to Retirement = Target Retirement Number

Let's work backwards:

If you have $300,000 today
You expect 7% annual returns
You're targeting $1,000,000 for retirement
Your money will reach $1,000,000 in approximately 19 years

That means at age 46 (if you started at 27), you could coast to $1 million by 65.

The real magic? You're no longer stressed about whether this month's market downturn derails your plan. You're already ahead.

Setting Up Your Coast FIRE Calculator in Google Sheets

Let's build a tracker that does this math automatically—then shows you your coast date instantly.

The Basic Formula Approach

Column Setup:

A: Your current age
B: Target retirement age
C: Current investment balance
D: Expected annual return (%)
E: Target retirement amount
F: Years to retirement = B - A
G: Future value of current investments
H: Coast FIRE date

The Key Formula (for column G - Future Value):

=C * POWER(1 + D/100, F)

This tells you: "My current balance, grown at my expected return rate, for the years remaining until I want to retire."

Interpreting the Result:

If G > E (Future Value > Target Amount):

You've already coasted
Your money will overshoot your target
Consider increasing your retirement goal or reducing your working years

If G = E (approximately):

You're at your coast FIRE threshold today
Stop contributions and let compound growth work

If G < E:

You're not at coast FIRE yet
Continue your current contribution strategy
This calculator shows you how close you are

The Advanced Tracker with Multi-Scenario Planning

This is where Google Sheets really shines—you can model different scenarios without complex spreadsheet work.

Set up these sections:

Your Current Situation:

Current Age | Current Investment Balance | Annual Contributions | Expected Return | Retirement Goal | Target Retirement Age

Coast FIRE Scenarios:

Scenario	Current Balance	Annual Return	Target Number	Retirement Age	Coast Date	Years to Coast
Conservative (5%)	$300,000	5%	$1,000,000	65	[Formula]	[Formula]
Moderate (7%)	$300,000	7%	$1,000,000	65	[Formula]	[Formula]
Optimistic (9%)	$300,000	9%	$1,000,000	65	[Formula]	[Formula]

The Coast Date Formula:

=A / LOG10(1 + B)

Where:

A = LN(Target Number / Current Balance)
B = Annual Return Rate

Or more practically, use:

=NPER(annual_return, 0, -current_balance, target_number)

This gives you the exact number of years until your current investments reach your target.

Real Examples: When Does Coast Actually Happen?

Example 1: The Early Investor

You're 32 with $350,000 saved. You want $1.2 million by 65 (33 years).

At 7% annual returns:

Your $350,000 grows to approximately $3.2 million by age 65
You've already exceeded your goal
You coasted at age 32

Decision: Drop to part-time work immediately, or shift contributions to other goals (travel fund, house fund, tax-advantaged accounts).

Example 2: The On-Track Saver

You're 42 with $400,000. Target: $1.5 million by 65 (23 years).

At 6% annual returns:

Your $400,000 grows to approximately $1.67 million by age 65
Just slightly above your goal
You're at coast FIRE today

Decision: Stop aggressively saving and reallocate mental energy to skill development, relationships, or lower-stress work.

Example 3: The Accelerator

You're 35 with $250,000. Target: $2 million by 65 (30 years).

At 8% annual returns:

Your $250,000 grows to approximately $1.2 million by age 65
You're short by $800,000
You're not at coast FIRE yet—need approximately 45 more years to coast (age 80)

Decision: Continue contributions. OR increase expected return through investment strategy. OR adjust retirement goal down to match projected balance. OR extend retirement age.

From Coast FIRE to Full FIRE: The Three-Phase Strategy

Phase 1: Accumulation (Until Coast FIRE)

Your mission: Build the nest egg that will coast to your target.

Maximize contributions
Focus on consistent, automated investing
Track expenses ruthlessly (this is where Expense Sorted plays a critical role)
Prioritize high-income years

Why tracking matters: The difference between spending $50,000 and $60,000 annually is $10,000 extra to invest. At 7% returns over 20 years, that extra $10,000/year becomes nearly $400,000. Precision expense tracking isn't just about knowing where your money goes—it's about compounding that difference into freedom.

Phase 2: Coast FIRE (Until Full FIRE)

Your mission: Let compound growth do the heavy lifting while you live differently.

Cut expenses (or keep them steady while income options are more flexible)
Transition to part-time, contract, or passion-project work
Rebuild psychological capital and reduce burnout
Explore lower-stress career paths
Continue investing but remove the pressure

Your investments compound at their historical average. Market downturns don't matter—you're not depending on near-term growth. You have time.

Phase 3: Traditional FIRE (Retirement)

Your mission: Live on your investments, knowing your coast strategy got you here.

Begin calculated withdrawals
Adjust portfolio allocation for income generation
Enjoy the fruits of your discipline

Integrating Coast FIRE with Your Expense Tracking

Here's where this becomes truly powerful: Your coast FIRE date depends entirely on your current investment balance. And your investment balance depends on how much you've saved. And savings depends on the gap between income and expenses.

This is why tracking every dollar matters.

The connection:

Track expenses obsessively (reduce them by $100/month)
Invest that $100/month difference
$1,200/year extra compounds to $5,000-$10,000 over a decade
That's potentially 1-2 years off your coast FIRE date
You gain a decade or more of career flexibility

Use an integrated spreadsheet that connects:

Monthly expense tracking (from your bank CSV imports)
Savings rate calculation
Investment growth projections
Coast FIRE date visualization

When you see "I just moved my coast date forward by 6 months through expense optimization," suddenly frugality isn't deprivation—it's freedom math.

Common Coast FIRE Questions

Q: What if the market crashes? A: That's the beauty of coast FIRE. If you're already coasted, market timing becomes irrelevant. Your $300,000 might drop to $250,000 in a downturn, but you still have 20 years for it to recover to your target. You can weather crashes that would devastate someone still in the accumulation phase.

Q: Can I adjust my coast date? A: Absolutely. Change any variable:

Increase savings today (move coast date backward)
Increase expected return (through investment strategy)
Decrease retirement target
Extend retirement age
Combine approaches

Q: Should I stop investing after coast? A: No—continue investing, but without pressure. You might shift to:

Tax-advantaged retirement accounts
Index funds with lower fees
Real estate
Side business income
Skills that command higher wages later

Q: How does coast FIRE relate to lean FIRE or barista FIRE? A: They're complementary:

Lean FIRE: Lower retirement target (e.g., $600,000 vs $1 million)
Barista FIRE: Part-time work that covers expenses, letting investments coast (very similar to coast FIRE, but you're earning something)
Coast FIRE: Investment-only growth, no contributions required

You might coast at $300,000 to $800,000 (lean FIRE target), then barista-FIRE from there, where part-time income covers living expenses.

Building Your Personal Coast FIRE Dashboard

Here's what to track in one visual dashboard:

Current Status
- Today's investment balance
- Retirement target
- Years to target retirement
Coast Calculation
- Current trajectory (will you coast?)
- Projected balance at retirement
- Coasting date (or "not yet")
Scenarios
- What if I save $500/month extra?
- What if returns are 5% instead of 7%?
- What if I extend retirement by 2 years?
Monthly Update
- New contributions
- Market growth
- Updated coast date

Formula to connect to your expense tracker:

=IF(C * POWER(1 + D, E) >= F, "Coast FIRE Achieved!", TEXT((NPER(D, 0, -C, F)), "0.0") & " years until coast")

This one formula tells you your entire coast FIRE story.

Your Path Forward

Coast FIRE represents something profound: the mathematical point where you've done enough. You've saved enough. You've built a big enough pile that compound growth becomes your coworker.

The freedom that awaits isn't necessarily retirement at 55. It's the freedom to work on your terms. To say no to bad jobs. To invest in relationships instead of just dollars. To figure out what actually makes you happy, knowing your financial security is already baked into the math.

Start your calculator today. Find your coast date. Then ask yourself: "What would I do differently if I knew my retirement was already guaranteed?"

That's the real power of Coast FIRE.