Coast FIRE: How Much You Need to Stop Saving Now

A 35-year-old household earning $150k+ with $400,000 already invested may never need to save another dollar for retirement — assuming a 65-year-old finish line, a 7% real return, and a $1.5M target. The same household targeting a 50-year-old finish line needs roughly $980,000 right now to stop. That gap — $400,000 versus $980,000 to hit the identical lifetime number — is the entire Coast FIRE decision compressed into two figures, and it is governed almost entirely by one variable most calculators bury: how many years of compounding you have left.

Coast FIRE is the point at which existing invested assets, left untouched and contributing nothing further, will compound to a full FIRE number by a chosen retirement age. You keep working — you simply stop saving for retirement and cover only current expenses. The arithmetic is a present-value discount, not a savings-rate slog, which makes it the cheapest milestone in the entire FIRE framework to reach and the easiest to miscalculate.

The numbers that matter

Source: Coast FIRE figures calculated via present-value formula (FIRE number ÷ (1+r)ⁿ); safe withdrawal rate per Pfau (2012), Journal of Financial Planning; return assumption per Vanguard historical equity data.

How the formula actually works

Coast FIRE inverts compound growth. Standard FIRE asks how much you must accumulate to withdraw from; Coast FIRE asks how much you need today so that growth alone reaches that accumulation target by a future date. The formula is a present-value discount:

Coast FIRE Number = FIRE number ÷ (1 + r)ⁿ, where r is the expected real return and n is years until retirement.

The FIRE number itself comes first. Annual retirement expenses divided by a safe withdrawal rate (SWR) yields the required portfolio. Bengen’s original 1994 research in the Journal of Financial Planning established 4% as the maximum initial withdrawal rate sustaining a 30-year retirement on a 50/50 stock-bond portfolio. Bengen recognized that plugging an average return into a spreadsheet ignores real-world volatility, which is why the rate sits below the long-run return. For early retirees facing 40-plus year horizons, the math tightens. Bengen himself showed that extending a horizon from 30 to 45 years reduced the safe withdrawal rate from 4.1% to 3.5%, and Pfau’s 2012 research found a 3.3% rate at a 95% confidence level for a 40-year horizon. This cluster uses 3.5% as the baseline for any retirement projected past 30 years — the gap between 4% and 3.5% is the difference between [the 4% rule and a more conservative draw](/tax-wealth/fire/4-percent-rule-vs-3-5-percent/), and at this audience’s spending levels it moves the FIRE number by hundreds of thousands.

Worked example. A household projecting $52,500 in annual retirement expenses, divided by 3.5%, produces a $1.5M FIRE number. At age 35 with 30 years to a 65 retirement and 7% real growth: $1,500,000 ÷ (1.07)³⁰ = $1,500,000 ÷ 7.61 = roughly $197,000. That household needs $197,000 invested today to never save again and still arrive at $1.5M in today’s purchasing power. With $197,000 invested at 35, the account grows to $1,500,000 by 65 at a 7% return with zero additional contributions.

Why the retirement age is the whole game

Most coverage frames Coast FIRE around the target portfolio. The target barely moves the Coast number compared to the time horizon. Drop the retirement age and the discount period collapses, and because compounding is exponential, the required principal balloons.

Source: Author calculations using Coast FIRE present-value formula, FIRE number ÷ (1.07)ⁿ. Figures rounded. Consistent with published Coast FIRE reference tables (UngrindFi, 2026; Wealthvieu, 2026).

Pulling the finish line from 65 to 50 nearly triples the cash you need on hand to coast. The financial gap between retiring at 45 and 55 is not linear — it is exponential, and the Coast number is where that nonlinearity shows up most brutally. A household that can stop saving at $197,000 for a 65 retirement is staring at $762,500 for a 45 retirement of the same lifestyle.

Finluxy FIRE Timeline Estimate

The Finluxy FIRE Timeline Estimate measures years from current financial position to full FIRE, assuming net investable assets plus annual savings compound at 7% real until the portfolio equals annual expenses divided by a 3.5% SWR. Coast FIRE is a waypoint on that timeline — the moment continued saving becomes optional. The table below models three spending profiles for a representative $150k+ household with $400,000 in net investable assets (liquid plus investment accounts, excluding primary home equity) saving $60,000 per year.

Source: Author calculations. FIRE number = annual expenses ÷ 3.5% SWR. Coast number = FIRE number ÷ (1.07)²⁰. Timeline = years for $400k + $60k/yr contributions to compound at 7% real to the FIRE number. Lean FIRE defined as sub-$40k annual spend; fat FIRE as $100k+ annual spend.

The lean FIRE household has already passed its age-55 Coast number — its $400,000 exceeds the $295,000 threshold, meaning it could stop retirement saving today and still reach $1.14M by 55. The fat FIRE household, by contrast, needs $886,000 to coast to the same age and is not close. For a $150k+ earner, the fat FIRE column is the relevant one, and it exposes how much [fat FIRE at this income level](/tax-wealth/fire/fat-fire-150k-income-guide/) demands before coasting becomes available — well into seven figures of invested assets.

The conservative-return adjustment most people skip

Here is what the standard Coast FIRE pitch overlooks: the formula assumes a constant 7% real return every year from now until retirement, and that assumption is most dangerous precisely at the moment of coasting. Once you stop contributing, you lose the single most powerful defense against a bad market — fresh capital buying in at low prices. A household that hits its Coast number and quits saving right before a multi-year drawdown has no dollar-cost-averaging mechanism to recover. The portfolio must claw back on its own.

This is sequence of returns risk migrating into the accumulation phase, where it is rarely discussed. The coast calculation assumes a constant return; if markets decline significantly in the early years after reaching Coast FIRE, the portfolio may not recover to the target by retirement. The practical fix is to discount at a lower rate. A conservative approach uses 5% to 6% instead of 7% when calculating the Coast FIRE number to build in a buffer. The cost of that buffer is steep:

Source: Author calculations, FIRE number ÷ (1+r)²⁰. Real return range per Wealthvieu (2026) conservative Coast FIRE guidance; 7% real baseline per Vanguard historical US equity data.

Shifting the assumption from 7% to 5% raises the same household’s Coast number by roughly 46%, from $387,500 to $565,600. The distinction here is real return versus nominal return — the 7% figure is already inflation-adjusted, so layering an additional inflation haircut on top would double-count. Households that run Coast numbers off nominal 10% returns are systematically understating what they need, often by a third or more.

Where $150k+ households actually stand

Net investable assets, not net worth, drive the Coast calculation — primary home equity does not compound into a withdrawable portfolio. That distinction matters at this income level because high earners frequently carry substantial home equity that inflates net worth while contributing nothing to a FIRE number. The Federal Reserve’s 2022 Survey of Consumer Finances reports mean household net worth of $1.06 million and median before-tax income of $70,260, with the top 10% of households holding 67% of total household wealth. A $150k+ earner sits comfortably in that top decile, but the relevant question is how much of any balance sheet is liquid and invested versus locked in housing.

The SCF data also shows retirement accounts were held by 54% of families in 2022, behind bank accounts at 99%. For households that do hold them, individual-account retirement assets made up 65% of financial assets at the median among owning families in 2022. The takeaway for coasting: most invested wealth for high earners is concentrated in tax-advantaged retirement accounts, which is exactly the capital that compounds untouched in a Coast FIRE plan — but also exactly the capital subject to early-withdrawal friction if the coast period ends in genuine early retirement rather than continued work.

Methodology

What this means at $150k+

Coasting is a leverage decision disguised as a savings decision. For a household pulling $150k+, the binding constraint is rarely whether you can reach a Coast number — it is which retirement age you anchor to, because that single choice swings the required principal by 3x or more. A high earner who front-loads aggressively in their early thirties can plausibly hit an age-60 Coast number around $276,000 and then redirect what was retirement savings toward a lower-stress career, a sabbatical, or simply higher current spending. The trade-off is concrete: every year you bring the retirement target forward, you forfeit a year of compounding and must replace it with cash on hand today.

For this income bracket the more honest framing is fat FIRE coasting, where $100k+ in annual retirement spending pushes the FIRE number past $3M and the age-55 Coast threshold near $886,000. Reaching that is not a mid-thirties event for most — it implies a decade-plus of disciplined accumulation first. The households that benefit most from running these numbers are the ones who discover they have already passed a lean or standard Coast threshold without realizing it, and have been over-saving against a target compound growth would have hit on its own. The cost of not running the calculation is years of unnecessary frugality; the cost of running it wrong — off nominal returns, off a 4% rate for a 45-year horizon, or off net worth instead of net investable assets — is arriving at 55 with a portfolio that quietly fell short while no fresh contributions were there to catch it.