Coast FIRE Calculator

What "coasting" actually means

Most retirement math answers one question: how much do you need to have saved by retirement. Coast FIRE answers a different, more immediately useful question: how much do you need to have savedright now for compounding alone — with no further contributions, ever — to carry that balance to a full retirement number by the time you get there. The moment your invested balance crosses that line, every dollar you'd otherwise have funneled into retirement savings is freed up for something else: a lower-paying job you'd actually enjoy, a shorter work week, a career change, or simply spending more today, because the retirement leg of the plan no longer needs new fuel to reach its destination on time.

This is deliberately not the same claim as "you can retire" or "you can quit your job." Coast FIRE is a statement about one specific pot of money — your invested retirement savings — and one specific promise: growth alone gets it where it needs to go. It says nothing about your current income covering your current spending, health insurance, or anything else that a paycheck between now and retirement is still doing. See "Coast ≠ quit" below for why that distinction matters more than it sounds.

The math, shown in full

Everything on this page comes from four formulas, computed directly from your inputs — no hidden lookup tables, no black box:

realReturn = (1 + return/100) / (1 + inflation/100) − 1
fireNumber = max(0, annualSpend − annualBenefits) / (swr/100)
coastNumber = fireNumber / (1 + realReturn)^(retireAge − age)
reached = invested >= coastNumber

The real return converts your nominal (before-inflation) return assumption into an inflation-adjusted growth rate — because both annualSpend and the FIRE number itself are expressed in today's dollars, the growth rate carrying your invested balance toward that number has to be a real rate too, or the comparison would be apples to nominal-inflated oranges. TheFIRE number is the full nest egg your desired spending would require under your safe withdrawal rate, after subtracting whatever guaranteed benefit income (CPP, OAS, Social Security, a pension) already covers part of it. The coast number discounts that FIRE number back to today, using the real return over the years remaining until retirement — it's the exact balance that, left alone, compounds into the FIRE number right on schedule. And reached is simply whether your actual invested balance already clears that bar.

If you haven't reached it yet, the calculator also solves for the level real monthly contribution that would close the gap by your target retirement age — a standard future-value-of-an-annuity solve run against the real monthly rate, added on top of your invested balance's own growth:

invested × (1+realMonthlyRate)^months + monthly × (((1+realMonthlyRate)^months − 1) / realMonthlyRate) = fireNumber

where months is the number of months between now and your retirement age andrealMonthlyRate is the real annual rate converted to an equivalent monthly rate. Solve that equation for monthly and you get exactly the "Monthly needed to coast" figure above — the number that, if you kept contributing it every month between now and retirement, would let you hit the same FIRE number your coast number is already targeting. It's $0 the moment you're coasted, since there's nothing left to solve for.

A worked example

Run the defaults exactly as they load — a 30-year-old retiring at 65, spending $40,000/year in today's dollars, no benefits, $100,000 currently invested, at a 7% nominal return and 2.5% inflation with a 4% safe withdrawal rate — and here's what comes out: the real return works out to roughly 4.39%, the FIRE number is a clean $1,000,000 ($40,000 ÷ 4%), and discounting that back 35 years at 4.39% real puts the coast number at roughly $222,300. With only $100,000 currently invested, that's well short — the verdict tile reads "not yet coasted," the gap sits around $122,000, and the monthly- needed figure shows what it would take to close it by 65. Raise "Currently invested" past roughly $222,300 in the form above and watch the verdict flip: gap and monthly-needed both drop to $0, because at that point growth alone — no more contributions required — already gets there.

Every default, and why it's set where it is

• 7% annual return. A nominal, long-run planning assumption roughly in line with historical diversified-equity averages including dividends, used consistently across this site's other calculators (see DEFAULTS in the shared constants file) so numbers stay comparable across pages. It's a planning assumption, not a forecast — stress-test it lower if you want a more conservative coast number.
• 2.5% inflation. A moderate long-run inflation assumption, paired with the 7% return to produce a real return in the low-to-mid single digits — close to the range most retirement planning literature treats as a reasonable long-run real-return expectation for a diversified portfolio.
• 4% safe withdrawal rate. The classic "4% rule," fully adjustable — see the "What return/SWR should I use?" FAQ below. A lower SWR (more conservative) raises the FIRE number and pushes the coast number further out; a higher SWR does the opposite.
• Age 30, retiring at 65 — a 35-year horizon. Long enough for the gap between "coast number" and "FIRE number" to be visible and meaningful, since that gap shrinks toward zero as retirement approaches (there's less time left for compounding to do the work, so the coast number rises toward the full FIRE number the closer you get).
• $40,000 annual spending, $100,000 currently invested. Chosen so the default view deliberately lands on "not yet coasted" rather than either extreme — close enough to the coast number that raising "Currently invested" a realistic amount flips the verdict tile, which is the whole point of an interactive calculator rather than a static answer.
• CPP/OAS annual defaults ($10,524 / $9,024). The CRA's published average CPP retirement pension for new beneficiaries at 65, and the maximum OAS pension for ages 65-74, each ×12 to convert the monthly figures used elsewhere on this site into the annual figure this calculator's benefits field expects — see BENEFIT_DEFAULTS in the shared constants file for exact sourcing and retrieval dates, and the "Does CPP/OAS count?" FAQ below for why they're averages/ maximums rather than guarantees.

How CPP, OAS, and a pension change the Canadian answer

Turning on "Canada CPP/OAS mode" doesn't change any of the four formulas above — it changes one input to them: annualBenefits. CPP, OAS, and an optional pension field are summed together and subtracted from your annual spending before the FIRE number is even calculated, because guaranteed government (and employer, for a pension) income covers part of your spending automatically, before a single dollar of your own portfolio gets touched. A smaller required FIRE number means a smaller coast number too, since coastNumber scales directly with fireNumber — so for a Canadian retiree, CPP and OAS don't just add income on top of the plan, they shrink how much the portfolio itself has to carry.

Concretely: with the defaults' $40,000 spending target, adding roughly $12,000/year of combined CPP and OAS (close to this calculator's own defaults) drops the required FIRE number from $1,000,000 to $700,000 — a 30% reduction — and the coast number falls by the same proportion, from roughly $222,300 to about $155,600. That's the entire mechanism: benefits reduce the gap the portfolio has to close, nothing more exotic than that. The defaults here are deliberately conservative about what they claim — CPP defaults to the CRA's average new-beneficiary amount, not the maximum, and OAS defaults to the maximum, which most recipients don't actually receive in full — so replace both with your own real numbers from a My Service Canada Account statement once you have them, and use the optional pension field for anything else guaranteed (a DB pension, an annuity, or — for a US filer using this same mode's mechanism — a Social Security estimate).

Coast ≠ quit

It's worth saying plainly, because it's the single most common misreading of this idea: being "coasted" is not the same as being able to stop working. It means one specific savings goal — retirement — no longer needs new contributions to hit its target on schedule, assuming the return and inflation you entered hold up over the decades between now and retirement, which is a real assumption carrying real risk, not a guarantee. It says nothing about whether your current paycheck covers your current rent, your health insurance, your kids' tuition, an emergency fund, or any other goal that isn't "retirement 20 or 30 years from now." Plenty of people reach their coast number and keep working full-time at the same job for years afterward, simply redirecting the money that used to go toward retirement savings into something else — a house down payment, more aggressive debt payoff, or a larger emergency fund — while the retirement account itself runs on autopilot in the background. Coast FIRE is permission to stop worrying about one part of the plan, not a green light to quit anything.

What this calculator doesn't model

This is a planning estimate, not financial advice, and not a substitute for a financial planner who knows your full situation. Specifically excluded: taxes on eventual withdrawal (this calculator shows pre-tax figures only, in today's dollars); market sequence-of-returns risk (both accumulation and "coasting" use a single flat real return, not a simulated range of possible market paths — a real portfolio doesn't grow at a smooth constant rate every single year, and a few bad years early in retirement can matter more than the long-run average suggests); CPP/OAS/Social Security claiming-age mechanics (benefit amounts here are fixed inputs, not computed from a claiming age); healthcare costs or other spending that might rise faster than general inflation; and any change in spending, income, or goals between now and retirement that would move the target this calculator is aiming at. Treat every output here as a starting point for a conversation with a licensed financial planner, not a filing-ready or investment-ready number.