Coastfire.info

The Coast FIRE Calculator — A Forecast in Compound Growth

When can you
stop saving
for retirement?

Find the moment your portfolio becomes large enough to grow into your retirement target on its own. Adjust your inputs, share the URL, and see exactly when compound growth takes the wheel.

§ IV.i · The Trajectory INFLATION-ADJUSTED · IN TODAY'S DOLLARS
§ IV.ii · The Anatomy of Compounding

Your contributions accumulate linearly. Compound growth does not. In your forecast, growth surpasses contributions around age 61 — that's the milestone working.

§ V · The Verdict

You are 32 years from Coast FIRE

At your current pace, you cross the milestone at age 62. From that day forward, you may stop saving for retirement and still arrive at your FIRE number on schedule.

§ VI · A Summary IN TODAY'S DOLLARS
Coast FIRE Nº
$272,322

at your current age

FIRE Number
$1,000,000

in today's dollars

Net worth
$1,007,036

projected at retirement

Annual income
$40,281

today's dollars

§ VII · Year-by-Year
Age Year Bal. coastingBal. if contributing Contrib./yr Cum. contrib. Growth Coast target
302026$50,000$50,000$0$0$0$272,322
312027$64,100$64,100$12,000$12,000$2,100$282,634
322028$78,734$78,734$12,000$24,000$4,734$293,335
332029$93,922$93,922$12,000$36,000$7,922$304,442
342030$109,685$109,685$12,000$48,000$11,685$315,969
352031$126,045$126,045$12,000$60,000$16,045$327,933
362032$143,025$143,025$12,000$72,000$21,025$340,350
372033$160,647$160,647$12,000$84,000$26,647$353,237
382034$178,937$178,937$12,000$96,000$32,937$366,612
392035$197,919$197,919$12,000$108,000$39,919$380,494
402036$217,620$217,620$12,000$120,000$47,620$394,901
412037$238,066$238,066$12,000$132,000$56,066$409,853
422038$259,287$259,287$12,000$144,000$65,287$425,372
432039$281,312$281,312$12,000$156,000$75,312$441,478
442040$304,170$304,170$12,000$168,000$86,170$458,195
452041$327,894$327,894$12,000$180,000$97,894$475,544
462042$352,517$352,517$12,000$192,000$110,517$493,550
472043$378,071$378,071$12,000$204,000$124,071$512,237
482044$404,593$404,593$12,000$216,000$138,593$531,633
492045$432,120$432,120$12,000$228,000$154,120$551,763
502046$460,688$460,688$12,000$240,000$170,688$572,655
512047$490,339$490,339$12,000$252,000$188,339$594,338
522048$521,112$521,112$12,000$264,000$207,112$616,842
532049$553,050$553,050$12,000$276,000$227,050$640,198
542050$586,198$586,198$12,000$288,000$248,198$664,438
552051$620,601$620,601$12,000$300,000$270,601$689,597
562052$656,306$656,306$12,000$312,000$294,306$715,708
572053$693,363$693,363$12,000$324,000$319,363$742,807
582054$731,824$731,824$12,000$336,000$345,824$770,933
592055$771,740$771,740$12,000$348,000$373,740$800,124
602056$813,168$813,168$12,000$360,000$403,168$830,420
612057$856,165$856,165$12,000$372,000$434,165$861,863
62§2058$900,790$900,790$12,000$384,000$466,790$894,496
632059$934,897$947,104$0$384,000$500,897$928,366
642060$970,296$995,172$0$384,000$536,296$963,517
65§2061$1,007,036$1,045,060$0$384,000$573,036$1,000,000

Each row is a single year of your forecast. The gold marker sits at your Coast FIRE milestone; from there forward, the contribution column drops to zero and compound growth carries the balance the rest of the way.

§ Appendix · I

On Coast FIRE

Coast FIRE is the moment your investments are large enough to grow into your full retirement target — your FIRE number — without any further contributions. From that point on, you can coast: keep working to cover today's expenses, but no longer save for retirement. Compound growth handles the rest.

It's a milestone within the broader FIRE movement (Financial Independence, Retire Early). Reaching Coast FIRE doesn't mean you stop earning. It means saving becomes optional, freeing you to take a lower-paying job, switch careers, take a sabbatical, or simply spend your full paycheck without sliding backward.

How the math works

Three numbers do all the work:

  • FIRE number — the portfolio size that funds your retirement spending forever, computed as annual spending ÷ safe withdrawal rate. At a 4% withdrawal rate, $40,000 of annual spending requires $1,000,000.
  • Real return — your investment return after inflation and fees. A 7% nominal return with 3% inflation and 0.1% fees yields a real return near 3.8%.
  • Coast FIRE number at any age — the FIRE number discounted backward by your real return. Reach this and growth alone gets you to retirement.
§ Appendix · II

The Method

Every figure in the calculator is reported in today's dollars, so the numbers stay meaningful regardless of how far away retirement is. Here's exactly what happens behind the scenes.

Real return

real_return = (1 + growth − fees) ÷ (1 + inflation) − 1

Subtracting fees from your nominal growth rate and then dividing through by inflation produces the inflation-adjusted return. This is the rate used for every projection in the chart.

FIRE number

fire_number = annual_spending ÷ safe_withdrawal_rate

The classic 4% rule, drawn from the Trinity Study, suggests a portfolio can sustain a 4% withdrawal rate adjusted for inflation across most historical 30-year retirements.

Coast FIRE number

coast_fire_number(age) = fire_number ÷ (1 + real_return)retirement_age − age

The FIRE number discounted by real return for the years remaining until retirement. The further out retirement is, the smaller the Coast FIRE target — compound growth has more time to work.

Projection

The chart simulates each year from your current age to retirement. Within a year, contributions are applied monthly and balances compound at (1 + real_return)1/12 − 1. Two scenarios run in parallel:

  • With continued contributions — you keep saving at your monthly rate through retirement.
  • Coasting — you stop contributing the year you cross the Coast FIRE target line. From then on, balance grows on its own.

Caveats

This is a planning tool, not a guarantee. Returns vary, inflation surprises, careers change. Use the calculator to explore scenarios, not to plan your life around a single number.

§ Appendix · III

Reader Queries

Common questions from the correspondence pile.

01

Is Coast FIRE the same as regular FIRE?

No. Regular FIRE means you have enough invested to cover all your living expenses forever — you can stop working entirely. Coast FIRE only requires enough invested for compound growth to reach your full FIRE number by your target retirement age. You still need a paycheck to cover current expenses, but you no longer need to save for retirement.
02

What growth rate should I use?

Most planners model 7% nominal growth for a globally diversified stock portfolio held over decades. The S&P 500 has averaged closer to 10% nominally and 7% real over a century, but past performance is not a guarantee. Pick a rate you can defend if your portfolio underperforms it for a decade.
03

Why use the 4% safe withdrawal rate?

The 4% rule comes from the Trinity Study, which examined historical US returns and found a 4% inflation-adjusted withdrawal rate sustained most 30-year retirements. For longer horizons or more conservative plans, many planners use 3.25% to 3.5%.
04

Should I keep contributing after I hit Coast FIRE?

You don't need to, but extra contributions compound powerfully. Continuing to invest can let you retire earlier than your target age, raise your retirement spending, or build a buffer against sequence-of-returns risk.
05

Are these numbers in today's dollars or future dollars?

Today's dollars. The calculator uses your real (inflation-adjusted) return, so the projected net worth represents purchasing power at today's prices, not the larger inflated figure your statement will show in 30 years.
06

What about taxes, social security, or healthcare?

They're not modeled here. Coast FIRE is a back-of-the-envelope milestone, not a complete retirement plan. For full planning, layer in your tax-advantaged account types (401k, Roth IRA, HSA), social security estimates, and healthcare costs separately.
§ Appendix · IV

Further Reading

Field notes from the editor's desk.

01

About coastfire.info

A free, inflation-adjusted Coast FIRE calculator from an independent software studio. No accounts, no paywall, no upsell — just the arithmetic, in plain view.

02

Contact

Real correspondence — the kind that improves a tool — is read and answered. Here is how to reach the people who build coastfire.info.

03

Coast FIRE Number by Age: The Full Table

The Coast FIRE number is a moving target. Younger means smaller. Higher spending means larger. Here is the full table — and what each cell actually means.

04

Coast FIRE for Couples: How to Run the Math Together

Most FIRE calculators model a single person. Real households have two — usually with different incomes, different appetites for risk, and different ideas of what 'enough' means. The math gets richer.

05

Is 7% a Realistic Stock Market Return Assumption?

Every FIRE calculator hides an assumption about the future. Seven percent is the polite consensus — and a number worth interrogating before you bet a working life on it.

06

Coast FIRE vs Barista FIRE vs Lean FIRE: How to Choose

Four flavors of financial independence, one decision: how much do you want to keep working, and what for? A compact field guide with the numbers.

§ Appendix · V

Colophon

A note on who built this, and why.

The Coast FIRE Calculator was built by Sandhill.Software, an independent software studio that makes small, considered tools. It is offered free to the Coast FIRE community — no signup, no paywall, no upsell.

Most retirement calculators are gated behind a financial planner, a brokerage funnel, or a subscription. The math behind Coast FIRE is straightforward enough that none of that should be necessary. This calculator does the arithmetic in your browser, leaves your inputs in the URL where you can bookmark or share them, and ships its formulas in plain view under The Method above. Nothing is sent to a server; nothing is stored.

If a number here surprises you, the assumption that produced it is one of nine inputs in the form above. Change it, watch the projection move, and form your own judgement. That is the only way a back-of-the-envelope tool earns its keep.

Get in touch

Found a bug, have an idea, or want to push back on the methodology? Write to coastfire@sandhill.software. Real correspondence — the kind that improves a tool — is read and answered.