Coast FIRE Calculator: Find Your Coast FI Number
Coast FIRE Calculator
Enter your details to find your Coast FI number, the age you'll hit it, and your inflation-adjusted glide path.
How to use this Coast FIRE calculator
Enter your current age, target retirement age, expected annual spending in retirement (today's dollars), your current invested assets (401(k), IRA, taxable brokerage — but not your home), and how much you're saving each month. Then adjust three assumptions: your expected investment return, inflation, and your chosen safe withdrawal rate.
The calculator instantly returns four numbers: your Coast FIRE number (how much you need invested today), your full FIRE number (the target at retirement), the age at which your current savings pace will hit Coast FIRE, and your projected portfolio balance at retirement. The chart plots your projected portfolio against the Coast FIRE line at every age — the moment the green line crosses above the blue line is the moment you've reached Coast FIRE.
What is Coast FIRE?
Coast FIRE (also written Coast FI) is the point at which your invested assets are large enough that compound growth alone — with no additional contributions — will grow to your full retirement number by your target retirement age. Once you've reached it, you can stop saving for retirement and use that cash flow for anything else: travel, a career change, a lower-paying passion job, part-time work, or higher current spending.
Coast FIRE is a variation of the broader FIRE movement (Financial Independence, Retire Early). Where traditional FIRE means you have enough to stop working entirely, Coast FIRE keeps you working — but only to cover current living expenses (NerdWallet).
The Coast FIRE formula, explained
Calculating your Coast FIRE number takes two steps. First, work out your full FIRE number using the 4% rule from the Trinity Study — a landmark 1998 paper that found a 4% inflation-adjusted withdrawal rate had a near-100% success rate over 30-year retirements (Bogleheads):
Second, discount that future target back to today using compound growth in reverse:
Where r is your expected real (inflation-adjusted) return and t is the number of years until retirement. Using a real return instead of a nominal one keeps every dollar in today's purchasing power, so you never have to guess future inflation manually — this is the same method used by WalletBurst and most academic FIRE calculators.
Coast FIRE example: the math step by step
Meet Priya, age 30, aiming to retire at 65. She spends about $50,000 per year now and expects roughly the same in retirement (in today's dollars). She uses an 8% nominal return and 3% inflation, giving a real return of 4.85%.
- Full FIRE number: $50,000 × 25 = $1,250,000
- Years to retirement: 65 − 30 = 35 years
- Growth factor: (1 + 0.0485)35 ≈ 5.19
- Coast FIRE number: $1,250,000 ÷ 5.19 ≈ $241,000
If Priya has $241,000 invested today, she can technically stop contributing and coast to $1.25M by 65. If she has $75,000, she is on the way — and if she keeps investing $1,000 a month, she'll cross her Coast FIRE line in her early 40s. The calculator above works out that exact crossover age for your inputs.
Coast FIRE vs Lean, Barista, Fat, and Regular FIRE
Coast FIRE is one of five common FIRE variants. They differ in target spending level and relationship to work:
| FIRE type | Portfolio target* | Still working? | Best for |
|---|---|---|---|
| Lean FIRE | $625k – $1M | No — but minimal spending | Extreme frugality; $25k–$40k/yr lifestyle |
| Regular FIRE | $1M – $2M | No — fully retired | Middle-class retirement; $40k–$80k/yr |
| Fat FIRE | $2.5M – $5M+ | No — luxurious retirement | Comfortable/travel-heavy lifestyle |
| Barista FIRE | Portion of full FIRE | Part-time (often for benefits) | Bridging health insurance / partial income |
| Coast FIRE | FIRE ÷ (1+r)years | Full-time — but no more saving | Career pivots, freedom to spend on now |
*Illustrative targets for a $40k–$100k annual spend. Actual numbers depend on your spending needs (FinancialAha, FireNum types).
The key distinction: Coast FIRE means you stop saving, Barista FIRE means you scale back working, and traditional FIRE means you stop both. Coast FIRE sits between them — more accessible than full FIRE because you don't need the whole $1.25M today, more patient than Barista because you keep a full-time income until you're ready to change gears.
Why the calculator uses a real (inflation-adjusted) return
Every dollar in this calculator is in today's purchasing power. That's because the growth engine uses your real return — not your nominal return. The relationship is:
An 8% nominal return with 3% inflation gives a 4.85% real return, not the simple 5% you'd get by subtracting. Using the real number automatically bakes in future cost-of-living increases, so your projected $1.25M FIRE target in 35 years is a $1.25M target in today's spending power, not in inflated future dollars. Since 1957, the S&P 500 has delivered about 10.5% nominally and 6.7% after inflation (Investopedia) — most planners use a conservative 5%–7% real return for Coast FIRE math.
Coast FIRE number by age (illustrative)
Here's how the same $1,250,000 FIRE target scales down at different ages, using a 5% real return and a retirement age of 65:
| Current age | Years to 65 | Growth factor | Coast FIRE number | % of full FIRE |
|---|---|---|---|---|
| 25 | 40 | 7.04 | $177,600 | 14.2% |
| 30 | 35 | 5.52 | $226,600 | 18.1% |
| 35 | 30 | 4.32 | $289,100 | 23.1% |
| 40 | 25 | 3.39 | $368,900 | 29.5% |
| 45 | 20 | 2.65 | $470,700 | 37.7% |
| 50 | 15 | 2.08 | $600,700 | 48.1% |
| 55 | 10 | 1.63 | $767,300 | 61.4% |
The lesson is stark: every five years you delay roughly doubles what you need to have saved. A 25-year-old needs about $178k, a 45-year-old needs almost $471k — and a 55-year-old aiming at the same lifestyle needs three-quarters of a million. This is why aggressive early-career saving is the single most effective Coast FIRE lever.
Coast FIRE pros and cons
✓ Advantages
- Frees up cash flow — the average Coast FIRE household reclaims $12k–$24k/year of former retirement contributions
- Removes retirement-saving pressure without early retirement risk
- Enables career pivots, sabbaticals, and lower-paying purpose work
- Compound growth does the heavy lifting
- Compatible with 401(k) match and HSA — no reason to leave free money on the table
✗ Risks
- Sequence-of-returns risk — a bad early market can derail the plan
- Assumes your real return holds for 25–40 years
- Retirement expenses may rise (healthcare, long-term care)
- Loses tax-advantaged contribution room (401(k), IRA)
- Behavioral risk — you may struggle to restart saving later
7 ways to reach Coast FIRE faster
- Max the 401(k) match first. Employer contributions are an instant 25%–100% return on your money.
- Push your savings rate above 25%. Every extra 5% of income shaves years off your Coast FIRE date.
- Automate contributions on payday. Behavioral research shows automated savers reach targets 30% faster than manual savers.
- Use tax-advantaged accounts. A Roth IRA compounds tax-free — a huge multiplier over 30 years.
- Keep fees under 0.20%. A 1% fee versus a 0.05% index fund can cost you 25% of your final balance over 40 years.
- Increase contributions with every raise. Direct at least half of each raise to investments before lifestyle inflates.
- Lower your target retirement spending. Cutting expected spend from $60k to $50k drops your Coast FIRE number by ~17%.
↑ Test these scenarios in the calculator
Coast FIRE calculator FAQ
What is my Coast FIRE number?
Your Coast FIRE number is (annual retirement spending × 25) ÷ (1 + real return)years to retirement. Once your invested assets equal that amount, you can stop contributing and compound growth alone will reach full FIRE by your target retirement age.
What is the Coast FIRE formula?
The formula is Coast FIRE = FIRE Number ÷ (1 + r)t, where FIRE Number is annual spending × 25 (the 4% rule), r is your real return, and t is years until retirement.
What return should I use in a Coast FIRE calculator?
Most planners use a real (inflation-adjusted) return of 5% to 7%. The S&P 500 has averaged ~6.7% real since 1957, so 5% is conservative, 7% is aggressive, and 6% is a middle-of-the-road planning assumption.
Is Coast FIRE realistic in 2026?
Coast FIRE is realistic if you save aggressively in your 20s and early 30s and can tolerate market volatility. Newer research puts the truly "safe" withdrawal rate closer to 3.7% for 30-year retirements, so many planners now use 3.5%–4% as a cushion.
Can I retire once I hit Coast FIRE?
No. Reaching Coast FIRE means you can stop saving for retirement — not stop working. You still need income to cover current living expenses until your portfolio grows to your full FIRE number.
Coast FIRE vs Barista FIRE — what's the difference?
Coast FIRE means you stop contributing but still work full-time. Barista FIRE means you shift to part-time work (often for health insurance) while the portfolio grows untouched. Coast FIRE is a savings-side milestone; Barista FIRE is a work-side milestone.
Does inflation affect my Coast FIRE number?
Yes — heavily. That's why the calculator uses a real return (nominal minus inflation). Using real returns keeps every dollar in today's purchasing power so you don't have to guess future cost-of-living adjustments.
How much do I need to save to reach Coast FIRE by 35?
Assuming a $50,000 annual retirement spend, a 5% real return, and retirement at 65, you'd need about $289,000 invested by age 35. That typically requires saving 25%+ of gross income starting in your early 20s.
Should I stop contributing to my 401(k) after Coast FIRE?
Not entirely. Most CFPs recommend at least capturing the full employer match since it's free money, and continuing HSA contributions if eligible. Then redirect the rest of what you were saving to short-term goals.
What if the market crashes after I hit Coast FIRE?
A market crash can push you back below your Coast FIRE line. That's why most planners recommend a 10%–20% buffer above the calculated number and continuing at least modest contributions to protect against sequence-of-returns risk.
Sources & methodology
- Bogleheads — Trinity Study & Safe Withdrawal Rates — bogleheads.org
- Investopedia — S&P 500 Historical Real Returns — investopedia.com
- NerdWallet — What is Coast FIRE (CFP interview) — nerdwallet.com
- FireNum — Coast FIRE Guide & FIRE Types — firenum.com
- WalletBurst — Coast FIRE Math & Inflation Handling — walletburst.com
Calculator uses the standard Coast FIRE formula with inflation-adjusted real returns. Results are educational estimates and do not constitute financial advice. Sequence-of-returns risk, tax treatment, and changing spending needs may materially affect real-world outcomes.