Coast FIRE is the milestone where your invested portfolio is already large enough that, with investment growth alone and no further contributions, it will grow to your full retirement target by the time you stop working. This calculator finds that number, tells you whether you have reached it, and shows what your current portfolio would grow to — useful for anyone pursuing financial independence who wants to know when they can ease off saving.
How it works
The calculation has two steps:
- FIRE number = annual spending ÷ withdrawal rate. At a 4% withdrawal rate this is 25× your annual spend.
- Coast FIRE number = the FIRE number discounted back to today using your expected real (after-inflation) return over the years until retirement:
Coast FIRE = FIRE number ÷ (1 + real return)^(years to retirement)
If your current portfolio is at least the Coast FIRE number, you are “coasting” and can stop contributing. The tool also projects what your current balance would grow to by retirement.
Worked example
Age 30, retiring at 65 (35 years), spending $40,000/year, 4% withdrawal, 5% real return:
FIRE number = 40,000 ÷ 0.04 = $1,000,000 growth factor = 1.05^35 ≈ 5.516 Coast FIRE = 1,000,000 ÷ 5.516 ≈ $181,290
Having about $181,290 invested today at age 30 means you can theoretically stop all new contributions and still reach $1,000,000 by age 65 through market growth alone. If your current portfolio is already at $250,000, you are well past Coast FIRE for this scenario — you could coast from here.
How time horizon dramatically changes the Coast number
The longer your runway to retirement, the smaller the amount you need today — because compound growth has more years to work. The Coast FIRE number drops steeply with more years remaining:
| Current age | Retirement at 65 | Years remaining | Coast FIRE (for $40k/yr, 4% WR, 5% real return) |
|---|---|---|---|
| 25 | 65 | 40 | ~$142,000 |
| 30 | 65 | 35 | ~$181,000 |
| 35 | 65 | 30 | ~$231,000 |
| 40 | 65 | 25 | ~$295,000 |
| 45 | 65 | 20 | ~$377,000 |
Reaching Coast FIRE at 30 is far easier than reaching it at 45, even though the full FIRE target is the same — which is the core insight the Coast concept offers.
What “real return” means and why it matters
The calculation uses a real return — your investment return after subtracting inflation. Using a real return means the Coast FIRE number is expressed in today’s purchasing power, so you do not need to separately adjust for inflation.
A commonly used real return assumption for a diversified equity-heavy portfolio is around 5–7%. Using a more conservative 4% real return raises the Coast FIRE number significantly (because growth is slower); using 7% lowers it. The choice of assumption is the biggest source of uncertainty in the result.
Coast FIRE vs. Lean FIRE vs. Barista FIRE
These are related but distinct strategies:
Coast FIRE is about contributions, not spending. You stop adding new money but continue working (and presumably earning) until retirement.
Barista FIRE (or semi-retirement) means leaving a high-stress full-time job for part-time or lower-intensity work that covers current expenses — leaving the invested portfolio untouched to grow.
Lean FIRE means retiring fully at a very low annual spend (often below $25,000/year), which means a smaller FIRE number is needed.
Coast FIRE is particularly appealing because it changes what you are optimising for right now: once you hit the Coast number, additional savings are no longer necessary for your retirement security — you can direct surplus income to other goals (buying a home, education, experiences, charitable giving) without jeopardising retirement.
Limitations to keep in mind
- The projection assumes a constant real return. Actual returns are volatile; a bear market shortly before retirement can significantly affect outcomes. The 4% withdrawal rate is based on historical data from primarily US markets and may not hold universally.
- The calculation does not account for Social Security, pension income, or other non-portfolio retirement income. If you will receive Social Security, your required portfolio FIRE number is lower than this tool shows.
- Tax treatment of withdrawals matters. A traditional 401k grows tax-deferred but withdrawals are taxed as income; a Roth account is after-tax. The tool works in pre-tax gross numbers; your actual spendable income from a given portfolio depends on account types and tax situation.