Coast FIRE Explained: Formula, Examples and Calculator
Coast FIRE means your current investments may be enough to grow into your future retirement fund without aggressive new contributions.
Financial independence is built from a simple relationship: how much you spend, how much you save, how your investments grow, and how much flexibility you need. The FIRE framework turns those variables into a target. Once you know the target, you can estimate the monthly investing required and the approximate timeline.
FIRE is not one single lifestyle. Some people want to leave work permanently. Others want career flexibility, part-time work, a lower-stress job, or the ability to say no to bad opportunities. The best FIRE plan matches money with the life you actually want.
How FIRE math works
The simplest FIRE formula is annual spending divided by withdrawal rate. If you spend $60,000 per year and use a 4% withdrawal rate, the estimated target is $1.5 million. If you use a more conservative 3.5% rate, the target rises to about $1.71 million. Small changes in assumptions can create large differences in required wealth.
Example: $60,000 ÷ 0.04 = $1,500,000
What makes a FIRE plan stronger
A stronger plan has margin. That might include a lower withdrawal rate, flexible spending, diversified investments, a cash buffer, part-time income, or delayed large purchases. FIRE is easier when expenses are realistic and the plan can adapt to market downturns.
- Track annual spending accurately.
- Separate essential expenses from lifestyle expenses.
- Use conservative assumptions for returns and inflation.
- Consider taxes and account access rules.
- Build a plan that can survive lower-return periods.
Comparison table
| Path | Main Idea | Best For |
|---|---|---|
| Coast FIRE | Invest enough early, then let compounding work | People seeking future flexibility |
| Full FIRE | Enough invested to stop working now | People seeking immediate work optionality |
| Barista FIRE | Partial work plus investments | People wanting semi-retirement |
| Traditional retirement | Work until normal retirement age | Lower planning intensity |
Worked numerical examples
Example 1: Basic FIRE number
If annual spending is $50,000 and the withdrawal rate assumption is 4%, the estimated FIRE number is $50,000 ÷ 0.04 = $1,250,000. This number is not a guarantee, but it gives a planning target.
Example 2: Lower spending changes everything
If spending falls from $50,000 to $40,000, the 4% FIRE number falls from $1,250,000 to $1,000,000. A $10,000 annual expense difference can change the target by $250,000.
Example 3: Savings rate impact
A household investing $1,500 per month will usually reach financial independence faster than one investing $500 per month, even if both earn similar returns. The gap grows because contributions and compounding work together.
Common FIRE mistakes
FIRE planning is powerful, but it can become misleading if assumptions are too optimistic or too rigid. The goal is not to build a perfect spreadsheet. The goal is to build a plan that can survive real life.
- Ignoring taxes: withdrawals, account types and location can change after-tax income.
- Using one return assumption: markets do not deliver smooth returns every year.
- Underestimating healthcare or insurance: early retirement can create coverage gaps depending on country.
- Forgetting inflation: future expenses may be higher than today's spending.
- Over-optimizing lifestyle: a FIRE plan that requires permanent deprivation may fail behaviorally.
- Not building flexibility: part-time work, lower withdrawals or delayed retirement can protect the plan.
Calculate your FIRE plan
Use the free MoneyMath FIRE Calculator to estimate your FIRE number, timeline, Coast FIRE progress and monthly investing target.
Open FIRE Calculator →Related FIRE guides
The Coast FIRE formula: how to calculate your number
Coast FIRE requires only two inputs: your full FIRE number and the years until you want to stop contributing. The formula:
Coast FIRE number = FIRE target ÷ (1 + annual return)years remaining
At 7% real annual return, this gives you the amount you need invested today to reach your FIRE target at a future date without ever contributing again.
Coast FIRE by age and FIRE target: a reference table
How much you need invested today to coast to different FIRE targets at different ages, assuming 7% annual real return and a final retirement at age 65:
| Current age | Years to coast | Coast to €500K | Coast to €750K | Coast to €1M | Coast to €1.5M |
|---|---|---|---|---|---|
| 25 | 40 years | €33,200 | €49,800 | €66,400 | €99,600 |
| 30 | 35 years | €46,600 | €69,900 | €93,200 | €139,800 |
| 35 | 30 years | €65,400 | €98,100 | €130,800 | €196,200 |
| 40 | 25 years | €92,000 | €138,000 | €184,000 | €276,000 |
| 45 | 20 years | €129,000 | €193,500 | €258,000 | €387,000 |
| 50 | 15 years | €181,000 | €271,500 | €362,000 | €543,000 |
The younger you reach your Coast FIRE number, the more compounding does the work. At 25, just €33,200 invested grows to €500,000 by 65 without another penny contributed. At 45, you need €129,000 for the same result — nearly 4× more — because you have 20 fewer years of compounding.
What changes after Coast FIRE — and what doesn't
Reaching Coast FIRE is a genuine milestone that changes your relationship with work. It doesn't mean you stop earning — it means you can stop worrying about whether you're earning enough for retirement. The practical changes:
| Before Coast FIRE | After Coast FIRE |
|---|---|
| Must maximise income and savings rate | Only need to cover current expenses |
| High-pressure job is financially necessary | Lower-paying work you enjoy is viable |
| Sabbaticals feel risky | Career breaks don't derail retirement |
| Every career decision filtered through income | Career decisions filtered through meaning and quality of life |
| Fear of redundancy affects wellbeing | Redundancy is manageable — you're already "funded" |
Coast FIRE vs Barista FIRE vs full FIRE: the spectrum
Coast FIRE sits in the middle of the FIRE spectrum. Understanding where it fits helps clarify what you're actually aiming for:
- Full FIRE: Portfolio covers 100% of living expenses at a 3.5–4% withdrawal rate. Never need to earn income again. Highest number required, maximum freedom.
- Barista FIRE: Portfolio covers most expenses, part-time or low-stress work covers the gap (€500–1,500/month). Named for the classic "barista" job: stable, enjoyable, covers basics. Portfolio can be 40–60% of full FIRE number.
- Coast FIRE: Portfolio will grow to full FIRE number on its own by retirement age. Still need to cover full current expenses through work. Portfolio is typically 10–30% of full FIRE number depending on age.
- Lean FIRE: Full FIRE achieved, but at minimal spending levels. True financial independence at the cost of very constrained lifestyle.
The Coast FIRE validation: what to check before declaring it
Before concluding you've reached Coast FIRE, run through this checklist:
- Use real (inflation-adjusted) returns, not nominal. 7% real vs 9% nominal gives very different Coast numbers over 30 years. The MoneyMath calculator uses real returns by default.
- Be conservative on return assumptions. Historical global equity returns average 6–8% real. Using 5–6% gives a safety margin for sequence risk and international market variance.
- Account for the full retirement duration. If you plan to retire at 55 and live to 90+, the portfolio needs to last 35–40 years. Use a 3.5% withdrawal rate, which increases your FIRE target and therefore your Coast number.
- Don't count on future contributions. Coast FIRE assumes zero additional investment. If you're likely to keep investing at a lower rate, that's fine — it makes your position even more comfortable — but the baseline calculation should assume zero.
- Factor in healthcare and state pension gaps. Early retirement before state pension age means private healthcare costs and no state pension income for potentially decades. These reduce the spending the portfolio needs to cover once state pension kicks in.
Worked example: reaching Coast FIRE at 35
Maria, age 35, €180,000 invested, targets full FIRE at 60
Full FIRE number: €36,000/year spending × 25 = €900,000
Years to target retirement: 25 years (age 35 to 60)
Coast FIRE number needed: €900,000 ÷ (1.07)25 = €900,000 ÷ 5.43 = €165,700
Maria's current portfolio: €180,000 — she has exceeded her Coast FIRE number by €14,300.
She can stop all retirement contributions immediately. Her €180,000 will grow to approximately €977,000 by age 60 at 7% — slightly above her €900,000 target — without another euro invested. She now only needs to earn enough to cover her €3,000/month living expenses.
Coast FIRE and career flexibility: the real benefit
The financial maths of Coast FIRE is straightforward. The harder-to-quantify benefit is what it does to your relationship with work. Once you've reached Coast FIRE, you know the retirement outcome is secured regardless of what happens in your career. That knowledge changes everything about how you approach work decisions — whether to take a risk on a new role, negotiate harder, take a career break, or move to a lower-paying job that's more fulfilling. The financial security of Coast FIRE is partly monetary and partly psychological: the removal of existential financial anxiety from every career decision you make.
Frequently asked questions
What is FIRE?
FIRE stands for Financial Independence, Retire Early. It is a framework for building enough invested wealth to make work optional.
What is the FIRE number formula?
A common estimate is annual expenses divided by withdrawal rate. For example, $50,000 divided by 4% equals $1.25 million.
Is FIRE safe?
No plan is risk-free. A safer FIRE plan uses conservative assumptions, flexible spending and room for unexpected costs.
Final thought
FIRE is not just about quitting work. It is about increasing control. The most useful FIRE plan is one that turns vague ambition into measurable numbers, then gives you enough flexibility to handle real life.