How to Calculate Your Coast FIRE Number — Even If You're Bad at Math
Want to retire early — without becoming a spreadsheet wizard or finance bro? Coast FIRE might be your path. And yes, it’s easier than you think.
The Dream: Stop Saving, Let Time Take Over
Imagine waking up tomorrow and knowing you never need to save another dime for retirement. Your current investments are already on track to grow — all on their own — into your future nest egg.
That’s the idea behind Coast FIRE. It’s not about retiring today. It’s about hitting a point of no return — where compound interest does the heavy lifting and you get to live life more freely now.
But how do you figure out if you’re there yet?
That’s where your Coast FIRE number comes in — and this guide will show you exactly how to calculate it, even if math isn’t your thing.
Why Traditional Retirement Advice Misses the Mark
Most retirement advice assumes one thing:
You’ll keep saving forever.
It tells you to max out your 401(k), keep stashing cash every year, and aim for some huge number — like $1.5 million — decades from now.
But if you're already investing in your 20s or 30s, there’s a smarter path. Coast FIRE shows that with enough early momentum, you can stop saving and still retire on time.
Instead of overworking and over-saving, you coast to retirement.
What Is the Coast FIRE Number?
Your Coast FIRE number is the amount of money you need invested today that will grow — without any additional contributions — to your full retirement target by the time you hit retirement age.
For Example:
Let’s say you’re 30 and want $1 million by age 60.
If your investments grow at 7% annually, the formula is:
Where:
- annual return rate (e.g. 0.07)
- number of years until retirement
So:
That means if you have $131,367 invested today, and you never add another dollar, you’ll still hit $1M by 60.
That’s the power of compound interest.
How to Calculate Coast FIRE (The Easy Way)
Forget spreadsheets and confusing math. Here’s the step-by-step version:
✅ 1. Define Your Retirement Goal
Most FIRE folks aim for $1 million – $1.5 million depending on lifestyle, geography, and healthcare needs.
Start with your personal number.
✅ 2. Choose Your Target Age
This is when you fully retire — often age 55–65 in Coast FIRE.
✅ 3. Estimate Investment Growth
Use 7% average return for stocks (S&P 500 historical average). Adjust down to 5–6% if conservative.
✅ 4. Plug into the Formula
Use the math above or skip straight to the Coast FIRE Calculator to do it instantly.
✅ 5. Compare to Your Current Investments
If you already have that amount invested — congrats. You’ve reached Coast FIRE.
Why Coast FIRE Works (And Traditional Saving Doesn’t)
📈 The Math Is On Your Side
Compound growth accelerates over time. The earlier you invest, the less you need to add later.
According to Fidelity, someone who invests $10,000 at 25 and stops contributing will have more at 60 than someone who starts at 35 and contributes $10,000 every year.
⏳ Time Becomes Your Best Ally
Coast FIRE isn’t about retiring tomorrow. It’s about making freedom your default path — as long as you don’t cash out early.
🧠 It Lowers the Mental Load
Once you know you’re on track, you can breathe. You might:
- Switch to a lower-stress job
- Take a sabbatical
- Start a side hustle
- Travel more
It’s not early retirement. It’s early peace of mind.
Common Coast FIRE Mistakes to Avoid
Even smart FIRE folks slip up. Watch out for these:
- Underestimating future expenses — account for inflation, healthcare, and lifestyle changes
- Overestimating returns — 7% is average, but markets fluctuate
- Forgetting about taxes — Roth IRAs and HSAs can help reduce future burdens
- Not staying invested — pulling money early breaks the compounding cycle
That’s why tools like coast-fire-calculator.com help you adjust assumptions and stay realistic.
Tools to Help You Stay on Track
You don’t need to build a spreadsheet or do any math. Use the free Coast FIRE Calculator to:
- Plug in your age, retirement goal, and returns
- Get your personalized Coast FIRE number
- See how close you are — and what changes matter most
It’s mobile-friendly, private, and made for FIRE nerds and normal humans alike.
What To Do Next
You now know how to calculate your Coast FIRE number — even if you hate math. Here’s what to do:
- ✅ Visit coast-fire-calculator.com
- ✅ Run your own numbers — it only takes 30 seconds
- ✅ Compare it to your current investments
- ✅ Adjust your savings, work goals, or lifestyle accordingly
- ✅ Bookmark the calculator — and check in once a year
You’re Closer Than You Think
Coast FIRE isn’t a fantasy. It’s math. And it’s closer than most people realize — especially if you started investing young.
You don’t need to hit $1 million today. You just need enough momentum for time to take over.
And now, you’ve got the calculator to prove it.
Try the Coast FIRE Calculator →