Coast FIRE vs Lean FIRE: Which Needs Less Money?

Coast FIRE needs far less money invested, and lean FIRE lets you stop working soonest. At a 5% real return, a 30-year-old needs about $136,000 invested to coast to a $30,000-a-year retirement at 65, against $750,000 to retire on that budget now.

At the 7% real that many coast calculators use, the same 30-year-old's lean coast number drops to about $70,000, and the free coast FIRE calculator runs it on your own age, budget and return.

Coast FIRE means your investments grow into your retirement pot on their own, so from that point you only earn what you spend. Lean FIRE means retiring early on a small budget, commonly under about $40,000 a year, with 25× that invested.

Every number in this post uses the same assumptions:

• Today's dollars and a 5% real (after-inflation) return, between the 3.5% real a year world stocks managed over the 25 years to the end of 2024 and the 6.6% US long-run figure.
• A target of 25 × annual spending (how to calculate your FIRE number).
• Full retirement at 65, a starting balance of $0 and contributions at the end of each year.
• No taxes, fees or sequence risk.

Coast FIRE vs Lean FIRE in one table

How the coast FIRE number works

Coast FI is the amount you need invested "such that if you didn't touch your nest egg" it would grow into your retirement pot, as CFP Zachary Ashburn puts it in Kiplinger. After that you still work, possibly for decades, but your job only has to cover today's bills and the retirement line in your budget goes to zero.

Coast number = FIRE target ÷ (1 + real return)^(years until retirement)

For a 30-year-old aiming at a $750,000 lean target at 65: $750,000 ÷ 1.05^35 = $135,968.

At age 30, a 4% real return raises the lean coast number to $190,062 and 7% roughly halves it to $70,247:

Over the long record, world equities returned 5.2% real a year from 1900 to 2024, and the US did 6.6% from 1900 to 2025. Vanguard's ten-year forecast for US stocks, as of September 2026, is 4.8% to 6.8% a year before inflation.

How much lean FIRE needs

Lean FIRE is regular FIRE on a smaller budget, with 25 × annual spending invested before you quit. A $30,000 budget means $750,000; $40,000 means $1,000,000. There is no official definition of "lean", but under about $40,000 a year is the line most sources draw, and $30,000 is roughly 37% of the $81,905 the average US household spent in 2025.

The 25× comes from the 4% rule, and the 4% rule was built for 30-year retirements. William Bengen's 1994 paper found a 4% inflation-adjusted withdrawal never ran out in under 33 years of US history. A lean retiree at 47 needs the money to last 40 years or more. In Early Retirement Now's backtest of 1871-2016 data, a 4% withdrawal from a 50/50 portfolio succeeded about 95% of the time over 30 years but only 65% over 60 years. At a 3.5% withdrawal rate, the same $30,000 budget needs about $857,000.

Average household healthcare spending was $6,470 in 2025 by the same BLS survey, about 22% of a $30,000 budget. Healthcare is one of the floor costs in Lean FIRE vs Fat FIRE: price your spending floor first. If your health cover comes with a job, retiring early means paying for it yourself.

The same $60k earner, run three ways

One person aged 30, with $60,000 a year take-home, nothing invested yet and a 5% real return, can take three routes:

Data: MFFT calculation; $60K take-home earner aged 30, 5% real return, target 25× spending, retire at 65, start $0, end-of-year contributions.

Lean FIRE and the regular coast route both ask for about half of take-home pay. Lean FIRE ends work at 47 on $30,000 a year. Coast-by-40 means 25 years of earning only what you spend, then a retirement on $50,000. Lean coast asks for $17,608 a year, under 30% of take-home, for ten years.

If the return comes in at 7% real instead, the lean route still takes 15 years and the two coast-by-40 savings drop to $16,669 and $10,002 a year. At 4% real it rises to $39,055 and $23,433. Coast is far more sensitive to the return than lean, because coast money has 25 more years to compound with nobody adding to it.

Coast FIRE number by age, lean vs regular target

Data: MFFT calculation; 5% real return, target 25× spending, retire at 65.

The number climbs about 28% for every five years you wait. If you have a pension or state pension coming, your target is smaller than 25× your spending and every row drops.

The coast calculator's advanced defaults are an 11% return and 2.5% inflation, about 8.5% real, which puts the age-30 lean coast number at $43,154. Set the return to 7.5% with 2.5% inflation to match the table above.

Lean coast FIRE, fat FIRE and barista FIRE

Lean coast means aiming to coast to a lean budget, which at 30 is $135,968 for $30,000 a year. Every $10,000 a year of retirement spending adds $250,000 to a full FIRE target and, in coast capital, the following amount by age:

Fat FIRE, at $100,000 a year, needs 25× or $2.5 million, and on the same assumptions its coast number at 30 is about $453,000. Barista FIRE, often confused with coast, means leaving the career once the portfolio covers part of your spending and a part-time job pays the rest (what is Barista FIRE, and Barista FIRE vs Coast FIRE side by side).

Which one fits you

Of the three routes for the $60,000 earner, lean FIRE is the only one that ends work before 65: $30,000 a year saved for 17 years, then out at 47. Lean coast costs $17,608 a year for ten years and nothing more for retirement after 40, but the paycheck has to cover spending for the 25 years after that.

A lean budget has less room for a bad year: a $30,000 retirement that meets a new roof, a car and a health bill in the same year can only draw on the portfolio. A coaster still has a salary to absorb those costs, and where health insurance comes with employment, usually keeps the cover too.

Coast carries more of the return risk: if the past 25 years' 3.5% real world-equity return repeated, a coast-by-40 pot planned at 5% would reach only 69.8% of its target by 65, and the lean coaster would retire on about $20,900 a year instead of $30,000. Re-checking the number every year and keeping some contribution going after you cross it is the case made in Coast FIRE isn't a permission slip.

Run both numbers on your own figures

The free FIRE planner shows one target and date at a time, so run it twice, lean budget then normal budget. Set the return to 7.5% with 2.5% inflation (its own FAQ suggests 5% real for a 60/40 portfolio) and compare the two dates. Then put the budget you would really retire on into the coast FIRE calculator to see how far you are from your stop-saving point.