Full retirement means your savings can fund your life. Coast FIRE means something gentler: your savings can grow into that retirement number by themselves, while you keep working just to cover today's bills. The Coast FIRE Retirement Calculator tests exactly that — whether you can stop saving now and still retire on schedule.

Give it your current age, your invested savings, the monthly expenses you expect in retirement, your assumed return, and the age you want to stop saving. It returns your Coast FIRE number, projects your savings to that finish line, and delivers a verdict: reached, or not yet.

What Does the Coast FIRE Retirement Calculator Do?

The calculator builds a complete Coast FIRE plan from five inputs. First it converts your monthly retirement expenses into a Coast FIRE number — the amount your portfolio must reach by retirement. Then it grows your current savings to the age you stop saving and compares the two.

The verdict is the headline: You have reached Coast FIRE means your savings will cover the number on their own, and Not at Coast FIRE yet means a gap remains.

How to Use the Coast FIRE Retirement Calculator

Enter your current age and the age you want to stop saving — the difference is the compounding runway, and every extra year multiplies the projected value. Be honest about the stop age: Coast FIRE only works if contributions actually stop then.

Add your invested savings today and your expected monthly expenses at retirement. These two numbers fight in opposite directions: more savings shrinks the gap, while higher expenses grow the target. Choose your return, press Calculate, and read the verdict alongside the rows.

Coast FIRE vs. Traditional FIRE

Traditional FIRE means hitting the full retirement number now and quitting work entirely. Coast FIRE means reaching the point where growth alone will deliver that number later, so work becomes a choice rather than a requirement.

The trade-off is trust. Traditional FIRE owns the number today. Coast FIRE owns a projection of the number tomorrow, and projections depend on the return rate behaving for decades.

The Coast FIRE Number Formula

Your Coast FIRE number comes from the 4% rule: you can safely withdraw 4 percent of your portfolio per year in retirement, so you need 25 times your annual spending invested. The formula is:

Coast FIRE number = annual retirement spending x 25

Spend $4,000 a month in retirement and the annual figure is $48,000, which makes the Coast FIRE number $1,200,000. Every dollar of monthly spending you cut removes $300 from the target — small lifestyle trims move the finish line more than most people expect.

The Projection Formula Behind the Verdict

Once the target is set, the calculator grows your current savings to the stop-saving age with compound interest. The formula is:

Projected value = current savings x (1 + r)^t

Here r is your expected annual return as a decimal and t is the years between your current age and the age you stop saving. $150,000 at 7 percent for 25 years becomes $150,000 x 1.07^25, which is $814,114.90. The verdict then compares that projection against your Coast FIRE number.

Worked Example: 35 With $150,000, Spending $4,000 a Month

A 35-year-old has $150,000 invested, expects to spend $4,000 a month in retirement, assumes 7 percent returns, and wants to stop saving at 60. The target: $4,000 x 12 is $48,000 a year, so the Coast FIRE number is $48,000 x 25, or $1,200,000.

The projection: 25 years of growth at 7 percent turns $150,000 into $814,114.90 — below $1,200,000, so the verdict is Not at Coast FIRE yet. The gap is $385,885.10, and the required lump sum today is $221,099.01. Continued saving is still required, but the compounding runway is doing real work.

Worked Example: 40 With $300,000, Spending $3,500 a Month

A 40-year-old has $300,000 invested, expects to spend $3,500 a month in retirement, assumes 8 percent returns, and wants to stop saving at 65. The target: $3,500 x 12 is $42,000 a year, so the Coast FIRE number is $42,000 x 25, or $1,050,000.

The projection: 25 years at 8 percent turns $300,000 into $2,054,542.56 — clearing $1,050,000 with room to spare, so the verdict is You have reached Coast FIRE. The surplus is $1,004,542.56, against a required lump sum of only $153,318.80. He can stop contributing today and take any job that covers his bills.

Worked Example: 30 With $60,000, Spending $5,000 a Month

A 30-year-old has $60,000 invested, expects to spend $5,000 a month in retirement, assumes 7 percent returns, and wants to stop saving at 60. The target: $5,000 x 12 is $60,000 a year, so the Coast FIRE number is $60,000 x 25, or $1,500,000.

The projection: 30 years at 7 percent turns $60,000 into $456,735.30 — far short of $1,500,000, so the verdict is Not at Coast FIRE yet. The gap is $1,043,264.70, and the required lump sum today is $197,050.68. Youth gives him 30 years of compounding, but the balance is too small and the spending target too high.

Worked Example: 45 With $400,000, Spending $4,500 a Month

A 45-year-old has $400,000 invested, expects to spend $4,500 a month in retirement, assumes 6 percent returns, and wants to stop saving at 62. The target: $4,500 x 12 is $54,000 a year, so the Coast FIRE number is $54,000 x 25, or $1,350,000.

The projection: 17 years at 6 percent turns $400,000 into $1,077,109.28 — short of $1,350,000, so the verdict is Not at Coast FIRE yet. The gap is $272,890.72, and the required lump sum today is $501,341.97. He is about 80 percent funded, and shifting the stop age to 65 would lift the projection to $1,282,854.19 — nearly erasing the gap.

The 4% Rule Behind the Number

The Coast FIRE number rests on the 4% rule, born from the Trinity Study: a retiree withdrawing 4 percent of the starting portfolio, adjusted for inflation each year, survived 30-year retirements in nearly all historical scenarios. Multiply annual spending by 25 and you get the portfolio that funds it.

The rule has honest limits: it was tested over 30 years, not 50, and early retirees face longer horizons. Conservative planners use 3.5 percent, which makes the target about 28.6 times spending — $48,000 of annual spending then needs $1,371,428.57, not $1,200,000.

Why the Stop-Saving Age Is the Hardest Input

The stop-saving age looks like a simple number, but it is really a promise about your future behavior. Coast FIRE only works if contributions actually stop then — zero new retirement money, not "a little less."

Push the stop age out by five years and two things improve at once: more contributions before the coast begins, and fewer compounding years needed afterward. Choose a stop age you would actually honor; a plan that assumes you stop at 60 while you keep quietly contributing has a hidden safety margin — which is fine, as long as you know it is there.

Common Coast FIRE Calculator Mistakes

The classic mistake is entering today's spending instead of retirement spending. A 35-year-old paying a mortgage and raising kids spends far more than the 60-year-old she will become. Overstating retirement expenses inflates the Coast FIRE number and can hide a verdict you have actually earned.

The second mistake is forgetting taxes in retirement. If your savings are pre-tax, the 4% rule's withdrawals are taxed too — $48,000 of spending needs more than $48,000 of withdrawals. Either gross up the spending input or accept that the number understates reality.

Where Coast FIRE Planning Is Useful

Coast FIRE planning shines at the moments when careers bend: the parent considering part-time work, the professional offered a lower-paying but saner role, the entrepreneur weighing a risky venture. The verdict reframes the question from "can I afford this" to "is my retirement already handled."

It is also the natural milestone between aggressive saving and full FIRE. Many savers discover they hit their coast number years before their full FIRE number — and that discovery is often the permission slip to enjoy the journey instead of grinding to the destination.

How to Interpret Your Result

Read the verdict, then read the margin. A "reached" verdict with a $1,004,542.56 surplus is a fortress; a "reached" verdict by a few thousand dollars is a coin flip riding on the return assumption. The gap or surplus row is the real answer; the verdict is just the headline.

Stress-test every answer: re-run with the return two points lower and monthly expenses 10 percent higher. If the verdict survives, your Coast FIRE status is durable.

What to Do After a "Reached" Verdict

First, verify before celebrating: re-check the return assumption, confirm the retirement spending figure, and make sure the invested savings you entered are really invested. A "reached" verdict built on optimistic inputs is a trap, not a trophy.

Second, decide what changes. Reaching Coast FIRE does not require quitting — it means retirement contributions become optional.

Frequently Asked Questions

1. What is Coast FIRE?

Coast FIRE is reaching the point where your current savings will grow into your full retirement number by themselves, with no further contributions. You keep working to pay today's bills, but your retirement is mathematically handled by compound growth.

2. How is Coast FIRE different from regular FIRE?

Regular FIRE means your savings can fund retirement today — you could quit work now. Coast FIRE means your savings will fund retirement later: you must keep earning to cover living costs, but retirement contributions become optional. Coast FIRE arrives years earlier with far less sacrifice.

3. Why does the calculator use 25 times spending?

It comes from the 4% safe withdrawal rule: withdrawing 4 percent of your portfolio per year historically sustained 30-year retirements. Since 4 percent is one twenty-fifth, the needed portfolio is 25 times annual spending. At a safer 3.5 percent, the multiplier becomes about 28.6 instead.

4. What counts as my monthly retirement expenses?

Your expected monthly spending once you stop working — housing, food, transport, insurance, healthcare, and fun — minus costs that will disappear, like mortgage payments or kids' expenses.

5. Can I include my home equity in savings?

No, unless you plan to sell and downsize in retirement. Home equity does not compound at your assumed return and you cannot spend it without selling or borrowing. Count only liquid, invested assets: retirement accounts, brokerage accounts, and similar.

6. What return should I assume?

Use a long-run real return: 5 to 7 percent for stock-heavy portfolios, 3 to 4 for conservative ones. Then test two points lower. Dropping the 35-year-old's return from 7 to 5 percent cut her projection from $814,114.90 to $507,953.24 — a $306,161.66 swing from one input.

7. Does inflation break the calculation?

Only if you mix real and nominal numbers. Use a real return against today's-dollar spending: your $4,000-a-month target stays in today's dollars and the return is after inflation. The 4% rule was designed in inflation-adjusted terms, so this pairing is exactly what the formula expects.

8. What if I cannot stop saving at my target age?

Then the verdict is conservative — continuing to contribute only adds margin. Enter the age you genuinely expect to stop. If life has you keep saving anyway, treat the extra contributions as a safety buffer on an already-good projection.

9. Should Social Security count toward the target?

Subtract the expected annual benefit from your annual expenses before the 25-times math.

10. Is the verdict a guarantee?

No. It is a projection resting on the return rate, the spending estimate, and decades of compounding behaving as assumed. Re-run it yearly, stress-test at lower returns, and keep a margin between your projected value and the target.

11. What if markets crash right after I reach Coast FIRE?

A crash at the verdict date is the worst case, because "reached" status depended on that moment's balance. This is why margin matters: the 40-year-old's $1,004,542.56 surplus survives a 30 percent crash, while a verdict reached by $5,000 does not. Build surplus before you celebrate.

12. Can couples calculate Coast FIRE together?

Yes — combine invested savings, use shared retirement spending, and use the later of the two stop-saving ages for the projection. Household Coast FIRE is the meaningful unit for couples planning together, since spending and savings are usually shared.

13. How does Coast FIRE handle healthcare costs?

Include realistic healthcare spending in the monthly expenses input, especially for early retirees who must buy insurance before Medicare age. Healthcare is the fastest-growing retirement cost, and underestimating it is the most common way Coast FIRE plans quietly fail.

14. What should I do with the gap amount?

The gap is your remaining savings target in today's dollars. Divide it by the years until your stop age for a rough annual savings goal — for the 35-year-old, $385,885.10 over 25 years is about $15,435.40 a year before growth. That turns an abstract verdict into a concrete plan.

15. Can I reach Coast FIRE and keep saving anyway?

Absolutely, and many do. Extra saving after reaching Coast FIRE buys a larger margin, an earlier full retirement, or a fatter retirement lifestyle. The verdict changes what saving means — from required to optional — not whether you may keep doing it.