Transparent method
The formula
Worked example
Example inputs
How to interpret the result
Coast FIRE asks a fundamentally different question than standard FIRE, not how much is needed to retire now, but how much needs to be invested today, with zero further contributions required, to grow on its own into a full retirement target by a chosen future age, which reframes the goal around a single lump sum rather than an ongoing savings rate.
Before you rely on it
What to check
Compare current invested assets against the modeled coast threshold specifically, since crossing that threshold is what defines coast FIRE, not the size of ongoing contributions.
The common error
Where people go wrong with coast FIRE calculator
Confusing coast FIRE with regular FIRE and expecting the target number to represent a full retirement portfolio needed today. Coast FIRE's number represents what's needed now assuming it grows untouched for years, not an amount meant to support withdrawals immediately.
Sensitivity evidence
How expected annual return changes the coast FIRE amount today
| Expected annual return | Coast FIRE amount today | Current cushion or gap |
|---|---|---|
| 4.0% | $562,675 | -$212,675 |
| 5.0% | $442,954 | -$92,954 |
| 6.0%worked example | $349,498 | $502 |
| 7.0% | $276,374 | $73,626 |
| 8.0% | $219,027 | $130,973 |
Every input, tested
Which input moves the coast FIRE amount today most
| Input | Tested from | To | Coast FIRE amount today at each end | Swing |
|---|---|---|---|---|
| Years until retirement | 19.0 years | 31.0 years | $495,770 to $246,382 | $249,387 (71%) |
| Expected annual return | 5.0% | 7.0% | $442,954 to $276,374 | $166,580 (48%) |
| Retirement portfolio target | $1,350,000 | $1,650,000 | $314,548 to $384,448 | $69,900 (20%) |
| Current invested assets | $315,000 | $385,000 | $349,498 to $349,498 | none |
Two variables at once
Coast FIRE amount today by expected annual return and retirement portfolio target
| Expected annual return \ Retirement portfolio target | $1,200,000 | $1,500,000 | $1,800,000 |
|---|---|---|---|
| 4.0% | $450,140 | $562,675 | $675,210 |
| 5.0% | $354,363 | $442,954 | $531,545 |
| 6.0% | $279,598 | $349,498 | $419,398 |
| 7.0% | $221,099 | $276,374 | $331,649 |
| 8.0% | $175,221 | $219,027 | $262,832 |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Retirement portfolio target | $1,500,000 |
| Years until retirement | 25.0 years |
| Expected annual return | 6.0% |
| Current invested assets | $350,000 |
| Coast FIRE amount today | $349,498 |
| Current cushion or gap | $502 |
Complete evidence
Full projection schedule
Show all 25 rows
| Period | Opening balance | Contribution | Growth | Ending balance |
|---|---|---|---|---|
| Year 1 | $350,000 | $0.00 | $21,000 | $371,000 |
| Year 2 | $371,000 | $0.00 | $22,260 | $393,260 |
| Year 3 | $393,260 | $0.00 | $23,596 | $416,856 |
| Year 4 | $416,856 | $0.00 | $25,011 | $441,867 |
| Year 5 | $441,867 | $0.00 | $26,512 | $468,379 |
| Year 6 | $468,379 | $0.00 | $28,103 | $496,482 |
| Year 7 | $496,482 | $0.00 | $29,789 | $526,271 |
| Year 8 | $526,271 | $0.00 | $31,576 | $557,847 |
| Year 9 | $557,847 | $0.00 | $33,471 | $591,318 |
| Year 10 | $591,318 | $0.00 | $35,479 | $626,797 |
| Year 11 | $626,797 | $0.00 | $37,608 | $664,404 |
| Year 12 | $664,404 | $0.00 | $39,864 | $704,269 |
| Year 13 | $704,269 | $0.00 | $42,256 | $746,525 |
| Year 14 | $746,525 | $0.00 | $44,791 | $791,316 |
| Year 15 | $791,316 | $0.00 | $47,479 | $838,795 |
| Year 16 | $838,795 | $0.00 | $50,328 | $889,123 |
| Year 17 | $889,123 | $0.00 | $53,347 | $942,470 |
| Year 18 | $942,470 | $0.00 | $56,548 | $999,019 |
| Year 19 | $999,019 | $0.00 | $59,941 | $1,058,960 |
| Year 20 | $1,058,960 | $0.00 | $63,538 | $1,122,497 |
| Year 21 | $1,122,497 | $0.00 | $67,350 | $1,189,847 |
| Year 22 | $1,189,847 | $0.00 | $71,391 | $1,261,238 |
| Year 23 | $1,261,238 | $0.00 | $75,674 | $1,336,912 |
| Year 24 | $1,336,912 | $0.00 | $80,215 | $1,417,127 |
| Year 25 | $1,417,127 | $0.00 | $85,028 | $1,502,155 |
Where the inputs come from
Retirement portfolio target is the amount you want at retirement age, often from the FIRE or retirement goal calculators. Years until retirement is how long the money can grow without new contributions, and expected return is your planning assumption after fees and, ideally, inflation. Current invested assets is what you already have. The calculation uses only growth, so any contributions you continue to make are extra margin.
Using the coast FIRE amount today in a real decision
It is a way to trade work intensity for time.
When the result stops applying
The result depends strongly on the assumed return and on markets cooperating: a lower return means a much larger coast number. You must still cover living costs from earnings until retirement, and inflation raises the target if it is stated in today's dollars. A sequence of poor early returns can leave you short. Retiring at coast age is not the same as being safe at the target.
What to compare it with
Find the target with the retirement goal or FIRE number calculators, and see how long the full plan takes on the FIRE calculator. The required retirement contribution page shows what you would need to save otherwise. Test a lower return to see how much margin your cushion has.
People also ask
Frequently asked questions
What is Coast FIRE?
It is the point at which your invested savings will grow to a full retirement target by themselves, so you can stop saving and only earn enough to pay current expenses.
How does the return assumption affect it?
Strongly. At a lower return the coast number rises sharply, so test a cautious rate to see whether your cushion holds.
Do I still need a job at Coast FIRE?
Yes, to pay living costs, but the job no longer needs to fund retirement, which allows lower-paying or part-time work.