Coast FIRE Calculator: Could You Stop Saving for Retirement Today?
Updated September 2026. This article is for educational purposes only and is not financial advice.
Coast FIRE calculator answers the smaller, sharper question behind “am I rich enough to retire”: whether the money you have already invested is enough for compound growth alone to carry it to your retirement number, with zero further contributions. What if the hardest part of saving for retirement is already behind you?
The math is almost rude in its simplicity. Your retirement target is 25 times your annual spend. Discount that number back to today at your expected real return. If what is invested now sits at or above the discounted number, you are coasting: you can stop saving for retirement and just cover today's bills.
Key numbers
- Coast number formula: FI number (25× annual spend) ÷ (1 + r)^n: Maya's: $1,250,000 → $230,311 at 7% over 25 years
- $150,000 invested = 65.1% of coast; gap = $80,311; crossover age 66
- At 35, each dollar added is worth ~$5.40 at 60 (1.07^25 ≈ 5.43)
- Trinity Study: 4% works about 95% of the time on a 50/50 mix over 30-year periods
- 1 percentage point of return moves the coast number by roughly $50,000 ($291K at 6% vs $183K at 8%)
What is Coast FIRE?
Coast FIRE is the point where your invested savings are large enough that compound growth alone will carry them to your full retirement number by your target retirement age: with zero further contributions. Once you hit it, you only need to earn enough to cover today's bills; the aggressive saving phase is over. It is not retirement: you still work. And it is not a promise: the growth is assumed, never guaranteed.
How does a coast fire calculator do the math?
Multiply your target annual retirement spend by 25: that is your FI number. Discount it back to today by dividing by (1 + your expected real return) raised to the years until retirement. Compare the result to what is invested now: at or above the coast number means you are coasting; below it shows the exact dollar gap. The four steps in detail:
- Set your FI number. Multiply your target annual retirement spend by 25. That is the 4% rule flipped around: $50,000 a year means a $1,250,000 target.
- Discount it to today. Divide that target by (1 + your expected real return) raised to the years until retirement. Seven percent real over 25 years shrinks $1,250,000 to $230,311.
- Compare it to what is invested now. At or above the coast number: you are coasting. Below it: the gap is the exact dollar shortfall, measured today.
- Read the verdict. “You're already coasting” or “Not coasting yet: you need $X more invested today.” Plus your crossover age: when your current balance reaches the full number untouched.
What is an example of a Coast FIRE calculation? ($50,000, 7%, and $230,311)
Take Maya. She is 35, has $150,000 invested, wants to spend $50,000 a year starting at 60, and assumes a 7% real return. Her FI number is $1,250,000 (50,000 × 25), and she has 25 years of compounding ahead. Discounted: 1,250,000 ÷ 1.07²⁵ = $230,311. That is her coast number: left alone at 7% real, it becomes $1,250,000 exactly when she turns 60.
She has $150,000. Progress: 150,000 ÷ 230,311 = 65.1%. Gap: $80,311. Verdict: not coasting yet: she needs $80,311 more invested today. Every extra dollar she invests now is worth about $5.40 at 60, because 1.07²⁵ ≈ 5.43. That is the part most people miss: at 35, each dollar added buys five dollars of retirement.
Her crossover age is 66: if she never saves another dollar, her $150,000 still reaches $1,250,000: six years after her target. That gap is exactly what the $80,311 closes. And if closing the gap means choosing between extra debt payments and extra investing, our pay-off-debt-or-invest calculator settles that trade in 60 seconds.
One more honest note: the number depends on years of runway, not birthdays. A 40-year-old targeting 65 with the same spend and return gets the same $230,311. Time does the discounting, not age.
I built the Coast FIRE Calculator to run exactly this math: five inputs in, coast number, progress, gap, crossover age, and a 40-year projection with the coast line drawn on it. It is an Excel spreadsheet with no macros, US$6.99, and it does one job.
What is the 4% rule behind Coast FIRE?
The 25× target comes from the 4% rule. Financial planner William Bengen published the original research in the October 1994 issue of the Journal of Financial Planning: testing every rolling 30-year period from 1926 onward, a 4% initial withdrawal (adjusted for inflation each year) survived even the worst historical starting year. He called it the SAFEMAX rate. Four years later, three Trinity University professors extended the analysis in what became the Trinity Study: on a 50/50 stock-and-bond mix, 4% worked about 95% of the time over 30-year periods. And “about 95%” is doing real work in that sentence. The studies assume a 30-year horizon, U.S. historical returns, no taxes, and no fees. Early retirees face 40- to 50-year horizons, where most research puts the conservative number closer to 3.25–3.5%. And the 2024–25 updates genuinely diverge: Bengen himself raised his number to 4.7% with broader diversification, while Morningstar's forward-looking models cut theirs to 3.7% for new retirees. The coast number is a planning lens, not a promise: which is why the calculator lets you set your own return instead of hard-coding optimism.
What do people get wrong about Coast FIRE?
Three traps worth naming. First: no, coasting does not mean you can quit your job: you still need to cover today's bills in full. Second: the return is not guaranteed: one percentage point moves Maya's coast number by roughly $50,000. Third: being closer to retirement makes the number harder, not easier, because fewer years of compounding means a bigger lump sum today.
“I can quit my job.” No. Coasting stops the saving, not the earning. You still need to cover today's bills in full. What changes is the pressure: the retirement account no longer needs feeding, so a lower-paying job you actually like stops being a financial crime. If the number is close but not quite there, the fix is partly saving and partly income: running the real math on a second income is the natural next calculation.
“The return is guaranteed.” The whole number pivots on one assumption. At 6% real, Maya's coast number jumps to about $291,000; at 8%, it falls to about $183,000. One percentage point moves the answer by roughly $50,000. Run it at 6% if you want a cushion. The honest version of this math always shows its sensitivity.
“Closer to retirement means an easier number.” It is the reverse. Fewer years of compounding means a bigger lump sum today. A 25-year-old targeting $1 million at 65 needs only about $67,000 invested; a 40-year-old needs about $184,000. Starting early is the entire trick: which is also why the milestone feels reachable. The number is small when you are young.
The same one-number thinking works closer to home: an emergency fund calculator turns savings divided by essentials into months of runway. Coast FIRE is that idea on a decades-long clock.
For the full math behind early retirement, the 4% rule, the Yield Shield, all of it, Quit Like a Millionaire is the playbook. Find it on our recommended reading shelf.
About Kollaz: Kollaz makes smart financial tools for modern money. This article's companion is the Coast FIRE Calculator spreadsheet: find your coast number, your progress, your gap, and your crossover age from five inputs.
Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point where your invested savings are large enough that compound growth alone will carry them to your full retirement number by your target retirement age: with zero further contributions. It is not retirement: you still work and cover today's bills; only the aggressive saving phase is over.
How do you calculate your Coast FIRE number?
Four steps: set your FI number (target annual retirement spend times 25, $50,000 a year means $1,250,000), discount it to today at your expected real return ($1,250,000 discounted 25 years at 7 percent real is $230,311), compare it to what you have invested now, and read the verdict, at or above the number means you are coasting.
Where does the 25x Coast FIRE target come from?
The 25x target comes from the 4 percent rule. Financial planner William Bengen's October 1994 research tested every rolling 30-year period from 1926 onward and found a 4 percent initial withdrawal, adjusted for inflation, survived even the worst historical starting year: the SAFEMAX rate.
Does reaching Coast FIRE mean I can quit my job?
No. Coasting stops the saving, not the earning: you still need to cover today's bills in full. What changes is the pressure: the retirement account no longer needs feeding, so a lower-paying job you actually like stops being a financial problem.
What do people get wrong about coasting?
Three traps: thinking you can quit working entirely, treating assumed growth as a promise rather than an assumption, and coasting on a number that is close but not quite there without a plan to close the gap.
Best Coast FIRE calculators in 2026
The best Coast FIRE calculators in 2026 let you adjust the two inputs that decide everything: your expected real return and your retirement spending target. A calculator locked to 7% returns and the 4% rule gives one answer; your life deserves a range. The calculator in this article shows how the coasting number moves as those assumptions change.
Sources
- Wikipedia: William Bengen (opened and read September 2026): Bengen's October 1994 Journal of Financial Planning paper “Determining Withdrawal Rates Using Historical Data”; the 4% SAFEMAX rate as a worst-case historical finding; the Trinity Study (1998) popularizing it. https://en.wikipedia.org/wiki/William_Bengen
- ChooseFI: “Am I Coast FIRE? How to Calculate When You Can Stop Saving (2026)” (opened and read September 2026): Coast FIRE definition as the point where invested savings grow to the full FI number without further contributions; the discount formula FI ÷ (1+r)^n; 7% real as the standard assumption; worked examples by age. https://choosefi.com/financial-independence/coast-fire
- CompoundLadder: “4% Rule 2026: Bengen's 4.7% Safe Withdrawal Update” (opened and read September 2026): Trinity Study success table (4% ≈ 95% on a 50/50 mix over 30 years); the 2024–25 revisions (Bengen 4.7%, Morningstar 3.7%, Vanguard 3.5–4.5%); the rule's assumptions: no taxes, no fees, 30-year horizon. https://www.compoundladder.com/guides/4-percent-rule
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