The Coast FI Number: How to Calculate When You Can Stop Saving and Let Your Investments Grow
Imagine this: You're 30 years old. You have $50,000 saved. You stop contributing to your retirement accounts entirely, right this second. No more 401(k) deposits. No more IRA contributions. Nothing.
By the time you're 65, thanks to compound interest at a conservative 7% return, that $50,000 grows to over $530,000. You haven't added a single dollar in 35 years.
That's the magic of Coast FI.
Coast FI is the point where your existing investments will grow to enough to support your retirement — without you ever contributing another dollar. Once you hit your Coast FI number, you can "coast" into retirement. You still need to cover your living expenses, but you no longer need to save for retirement. Every dollar you earn from that point forward is yours to spend, invest elsewhere, or use to upgrade your lifestyle.
In this guide, you'll learn exactly what Coast FI is, how to calculate your personal Coast FI number, and whether it's the right financial independence strategy for you.
What Is Coast FI?
Coast FI stands for "Coast Financial Independence." It's a subset of the broader FIRE (Financial Independence, Retire Early) movement, but with a fundamentally different philosophy.
Traditional FIRE says: Save aggressively until you have 25x your annual expenses, then retire completely.
Coast FI says: Save enough that your investments will grow to 25x your retirement expenses on their own. Once you hit that number, you can stop saving for retirement and just let time and compound interest do the rest.
The key distinction: Coast FI doesn't mean you can stop working. You still need to pay your current bills. But it means you can stop saving for retirement. That frees up 15-25% of your income for other priorities — whether that's travel, a down payment, starting a business, or just enjoying life more today.
Key Insight: Time is the most powerful force in investing. The younger you are when you reach Coast FI, the less money you need. A 25-year-old needs far less to Coast FI than a 45-year-old, because they have more years of compound growth ahead of them.
The Coast FI Formula
Calculating your Coast FI number is straightforward. You need three variables:
- Annual Retirement Expenses (E) — How much you'll need per year in retirement
- Years Until Retirement (T) — How many years until you plan to retire
- Expected Annual Return (R) — Your assumed investment growth rate
First, calculate your target retirement portfolio using the 4% Rule:
Target Portfolio = Annual Retirement Expenses × 25
(This is also known as your "FIRE Number")
Then, calculate how much you need today to reach that target:
Coast FI Number = Target Portfolio ÷ (1 + R)^T
Where R is your expected annual return (as a decimal) and T is years to retirement
This is the present value formula — it tells you how much you need invested today so that it grows to your target amount by retirement age.
Coast FI Examples by Age and Spending
Let's look at real numbers to understand how Coast FI works at different ages and spending levels.
| Your Age | Annual Expenses | Target Portfolio | Coast FI Number (7%) | Coast FI Number (10%) |
|---|---|---|---|---|
| 25 | $40,000 | $1,000,000 | $131,367 | $35,422 |
| 30 | $40,000 | $1,000,000 | $184,249 | $55,921 |
| 35 | $40,000 | $1,000,000 | $258,419 | $88,288 |
| 40 | $40,000 | $1,000,000 | $362,446 | $139,385 |
| 25 | $60,000 | $1,500,000 | $197,050 | $53,133 |
| 30 | $60,000 | $1,500,000 | $276,373 | $83,882 |
| 35 | $60,000 | $1,500,000 | $387,628 | $132,432 |
| 40 | $60,000 | $1,500,000 | $543,669 | $209,078 |
What This Tells Us: A 25-year-old with $40,000 annual expenses needs only ~$131,000 invested at 7% returns to Coast FI. That's achievable for many people. A 40-year-old with the same expenses needs ~$362,000 — still achievable, but requires more aggressive saving in the early years.
How to Calculate Your Personal Coast FI Number
Follow these steps to find your number:
Step 1: Estimate Your Retirement Expenses
Your retirement expenses will likely be different from your current spending. A common rule of thumb is 80% of your current income, but a more accurate approach is to track your current spending and adjust for retirement-specific changes:
- You'll no longer save for retirement (subtract 15-20% of income)
- Your mortgage might be paid off (subtract that monthly payment)
- Healthcare costs may increase (add $5,000-12,000/year)
- Transportation and work-related costs will decrease
- Travel and leisure spending may increase
Step 2: Choose Your Target Retirement Age
Traditional retirement age is 65, but Coast FI allows for early retirement if you started saving early enough. Typical Coast FI target ages range from 55 to 70.
Step 3: Select Your Expected Return Rate
A conservative estimate for a stock-heavy portfolio is 7% (the historical average of the S&P 500 is ~10% before inflation, so 7% accounts for ~3% inflation). More conservative investors might use 5-6%. Aggressive investors might use 8-9%.
Step 4: Apply the Formula
Let's walk through a full example:
Sarah's Coast FI Calculation:
Age: 30 | Target Retirement: 60 | Years to Grow: 30
Annual Retirement Expenses: $45,000
Target Portfolio: $45,000 × 25 = $1,125,000
Expected Return: 7% (0.07)
Coast FI Number: $1,125,000 ÷ (1.07)^30
$1,125,000 ÷ 7.612 = $147,790
Sarah needs $147,790 invested today to Coast FI. If she has that amount, she can stop all retirement contributions and still retire at 60 with $45,000/year in today's dollars.
Coast FI vs. Traditional FIRE: Key Differences
| Factor | Traditional FIRE | Coast FI |
|---|---|---|
| Time to achieve | 10-20 years of aggressive saving | 5-15 years (reached much sooner) |
| Savings rate required | 50-70% of income | 15-30% of income |
| Can you stop working? | Yes — completely | No — still need income for expenses |
| Can you stop saving? | Yes | Yes |
| Risk level | Higher (sequence of returns risk) | Lower (more time for recovery) |
| Lifestyle flexibility | Lower (need high income) | Higher (can downshift careers) |
The Barista FI and Lean FI Alternatives
Coast FI isn't the only "partial FI" strategy. Two related concepts are worth understanding:
Barista FI
Barista FI means you've saved enough that you can take a lower-paying, less stressful job (like working at Starbucks — hence the name) that provides health insurance and covers your reduced expenses. Your investments continue growing until you reach full FI. Barista FI typically requires more savings than Coast FI but less than full FIRE.
Lean FI
Lean FI means you have enough to retire on a minimalist budget — typically $20,000-40,000/year in spending. You've hit 25x your lean expenses but haven't accounted for lifestyle upgrades, large purchases, or financial buffers. Lean FI is a stepping stone to full FI.
Which Path Is Right for You? If you love your career, Coast FI might feel irrelevant — you'll keep saving anyway. If you're burned out but not ready to quit, Coast FI gives you permission to downshift. If you want maximum freedom as fast as possible, full FIRE is the goal. Most people find Coast FI is the first milestone they can celebrate on their FI journey.
The Case for Coast FI (Pros and Cons)
Why Coast FI Makes Sense
- Reached faster: Coast FI is achievable much sooner than full FIRE, giving you a sense of progress and freedom earlier in your journey.
- Reduces burnout: Knowing you no longer need to save for retirement reduces financial stress and allows you to take career risks.
- Allows career downshifting: You can switch to a lower-paying but more fulfilling job, start a business, or go part-time.
- Leverages time: The younger you are, the more dramatic the impact of compound interest on your Coast FI number.
- Lower savings rate requirement: Most people can reach Coast FI with a 15-25% savings rate, compared to the 50-70% needed for traditional FIRE.
The Risks and Drawbacks
- Market risk: A major market downturn early in your Coast FI journey could significantly delay your timeline.
- Inflation risk: Your "Coast" period could last decades — inflation erodes the purchasing power of your investments.
- Still need income: Coast FI doesn't mean you can quit working. You still need to cover daily expenses.
- Lifestyle creep: When you stop saving, it's easy to let spending inflate. You could end up needing more in retirement than you planned.
- Healthcare uncertainty: A serious health issue before retirement could derail your Coast FI plan.
How to Reach Coast FI: A Practical Strategy
Here's a step-by-step plan to reach your Coast FI number:
Phase 1: Build Your Foundation (Months 1-6)
- Create a zero-based budget to track every dollar
- Build a 3-6 month emergency fund in a high-yield savings account
- Pay off high-interest debt (credit cards, personal loans)
- Calculate your current savings rate
Phase 2: Accelerate Savings (Months 7-24)
- Maximize tax-advantaged accounts: 401(k), Roth IRA, HSA
- Consider low-cost index funds like those tracking the S&P 500
- Side hustles and additional income streams to boost savings
- Track your progress monthly against your Coast FI target
Phase 3: Coast (Year 2+)
- Once you hit your Coast FI number, redirect retirement contributions to other goals
- Consider a career shift to something more fulfilling
- Invest in experiences, relationships, and personal growth
- Rebalance your portfolio annually to manage risk
Coast FI Calculator: Quick Reference Table
Use this table to estimate your Coast FI number based on your age and target retirement spending:
| Retirement Expenses | Age 25 (35 yrs) | Age 30 (30 yrs) | Age 35 (25 yrs) | Age 40 (20 yrs) | Age 45 (15 yrs) |
|---|---|---|---|---|---|
| $30,000 | $98,525 | $138,187 | $193,814 | $271,835 | $381,310 |
| $40,000 | $131,367 | $184,249 | $258,419 | $362,446 | $508,414 |
| $50,000 | $164,209 | $230,311 | $323,024 | $453,058 | $635,517 |
| $60,000 | $197,050 | $276,373 | $387,628 | $543,669 | $762,621 |
| $80,000 | $262,734 | $368,498 | $516,838 | $724,892 | $1,016,828 |
| $100,000 | $328,418 | $460,622 | $646,047 | $906,115 | $1,271,035 |
Assumes 7% annual return. Years to retirement in parentheses.
Tools to Track Your Coast FI Progress
Several tools can help you track your journey to Coast FI:
- Personal Capital (Empower): Free net worth tracking with a retirement planner that can model Coast FI scenarios
- Compound Interest Calculators: Financial calculators help you visualize growth over time
- Portfolio Trackers: Monitor your investments with tools that show forward projections
- Spreadsheets: A simple Google Sheets or Excel model with the Coast FI formula gives you full control
Pro Tip: The best books on the FIRE movement — like "The Simple Path to Wealth" by JL Collins and "Your Money or Your Life" by Vicki Robin — provide deep frameworks for thinking about money, time, and freedom. Both are worth adding to your financial library.
Frequently Asked Questions
Is Coast FI the same as being financially independent?
No. Coast FI means your retirement is on autopilot, but you still need to earn money to cover current expenses. Full financial independence means your investments cover all your expenses, both now and in the future.
What happens if the market crashes right after I reach Coast FI?
Market downturns are the biggest risk to Coast FI. If you hit your number and then the market drops 40%, you're no longer on track. One strategy is to overshoot your Coast FI target by 20-30% to create a buffer against market volatility.
Can I Coast FI with a 401(k) or do I need taxable accounts?
You can Coast FI using retirement accounts alone. The key is that you've accumulated enough in your tax-advantaged accounts that they'll grow to your target without additional contributions. However, having some taxable brokerage savings gives you more flexibility if you want to access funds before retirement age.
Should I still contribute to my 401(k) after reaching Coast FI?
If your employer offers a match, you should almost certainly continue contributing at least enough to get the full match — that's free money. Beyond that, you have a choice: redirect funds to other goals (house, travel, business) or continue saving to reach full FIRE faster.
What's a realistic timeline to reach Coast FI?
For a typical person saving 15-20% of their income starting in their 20s, Coast FI is achievable within 10-15 years. Higher savings rates accelerate this dramatically — a 30% savings rate might get you there in 7-10 years.
Your Next Steps
Coast FI is one of the most liberating concepts in personal finance because it's achievable. Unlike full FIRE, which can feel like a distant fantasy requiring decades of extreme sacrifice, Coast FI is a milestone most people can reach with consistent, moderate effort over 5-15 years.
Here's what to do next:
- Calculate your number. Use the formula in this guide to find your Coast FI target.
- Track your current savings. Know exactly how much you have invested today.
- Create a plan. Determine how much you need to save each month to reach Coast FI by your target date.
- Optimize your investments. Ensure your portfolio is in low-cost, diversified index funds for maximum long-term growth.
- Revisit annually. Recalculate your Coast FI number each year as your expenses, timeline, and portfolio evolve.
The beauty of Coast FI is that it gives you permission to stop running on the hamster wheel while still securing your future. Once you hit that number, the hardest part is over. Time does the rest.
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