Coast FIRE means existing retirement investments may grow to a later target without major new contributions; it does not mean current living expenses are funded.
Coast FIRE asks whether money already invested for retirement could grow to the amount needed at a conventional retirement age, even if new contributions slow or stop. Current work still pays today’s bills. The value is flexibility: a person may choose lower-stress work, fund family goals, or reduce an aggressive savings rate.
The result is extremely sensitive to time and return assumptions. Nominal returns must not be compared with a target expressed in today’s dollars unless inflation is handled consistently. Fees, taxes, account restrictions, and changes in future spending also matter.
Work backward from a future target
Estimate retirement spending, subtract dependable income such as Social Security or pensions, choose a cautious withdrawal assumption, and calculate the portfolio needed at retirement. Then discount that amount back to today using a real return assumption—or inflate both the target and assets consistently using nominal figures.
Use multiple return cases
A single 7% projection creates false precision. Run conservative, base, and strong cases and include investment fees. Also test a retirement five years earlier or later. Time is the strongest Coast FIRE lever, which means an early reduction in contributions can be costly if assumptions prove optimistic.
Do not abandon useful contributions blindly
Employer matches, tax advantages, and low-cost automatic saving remain valuable after reaching a Coast estimate. Reducing contributions may be reasonable, but stopping everything removes margin. Review the calculation annually and after major changes in spending, family, income, or markets.
Worked example
Someone age 35 has $250,000 invested and wants $1.2 million in today’s dollars at 65. At a 4% real return for 30 years, $250,000 grows to about $811,000—short of the goal. At 5.5% real, it grows to about $1.25 million. That spread shows why declaring Coast FIRE from one optimistic return is risky.
| Assumption | Conservative | Base | Strong |
|---|---|---|---|
| Real return | 3% | 4% | 5% |
| Years | 30 | 30 | 30 |
| $250k future value | ~$607k | ~$811k | ~$1.08m |
| Action | Keep contributing | Measure gap | Add margin anyway |
Common mistakes
- Mixing nominal and inflation-adjusted dollars
- Using one optimistic return
- Forfeiting an employer match
- Ignoring future spending changes
- Never recalculating after reaching the label
Action checklist
- Calculate current net worth and twelve-month spending.
- Separate essential, flexible, and irregular costs.
- Calculate the invested balance required to reach the target without additional retirement contributions.
- Test lower returns, a later retirement date, and continued small contributions.
- Review progress annually instead of treating the coast date as permanent.
Related tools and guides
Sources and methodology
This guide uses planning principles and retirement research rather than promising a particular return or retirement date. Primary references include the SEC Investor.gov, IRS retirement-plan guidance, Social Security Administration, and Medicare. Tax rules, benefits, insurance costs, and market conditions change. Verify current rules and consider a fiduciary financial planner or tax professional before an irreversible decision.
Frequently asked questions
Is this a guarantee?
No. Reaching a Coast FIRE estimate means the current balance may grow to the target under stated assumptions; it does not guarantee the result.
How often should I review the plan?
Review at least annually and after a material change in balance, target spending, retirement age, or asset allocation.
What return should I assume?
Use a real return consistently, include fees, and test whether modest ongoing contributions materially improve the margin of safety.