Coast FIRE explained

Coast FIRE is a milestone in financial independence planning: the point at which your existing retirement portfolio is projected to grow to your full target through investment returns alone, without any additional retirement contributions. Reaching Coast FIRE does not mean you can stop working today — it means your retirement savings may be on track if you leave the balance invested until a later retirement age. The concept helps people evaluate career flexibility, partial retirement, and how much time compounds in their favor.

How the Coast FIRE threshold is calculated

Start with a retirement spending target and a withdrawal rate to determine your full FIRE number — the portfolio you would need at retirement to fund spending. Then discount that future amount back to today using the years until retirement and an assumed real return (return after inflation). If you plan to retire at 65, need $1.5 million then, and assume 5% real return over 25 years, the present value is the Coast FIRE threshold: the balance that could theoretically grow to $1.5 million without further contributions.

The Coast FIRE calculator performs this math with your current balance, target retirement age, spending, and return assumptions. Read our FIRE number guide for how spending and withdrawal rates feed the target.

Time and compound growth do the heavy lifting

Coast FIRE is especially sensitive to age and years until retirement. More time allows more compounding, which lowers the threshold balance required today. A 25-year-old with decades ahead needs a smaller current portfolio than a 45-year-old targeting the same retirement date. The SEC emphasizes that starting early gives investments more time to grow through compounding — the same principle Coast FIRE relies on.^[1][2]

Delaying the calculation by even a few years can require a substantially larger current balance because lost compounding years cannot be recovered without higher contributions or a later retirement date.

What changes after you reach Coast FIRE

Some people reduce retirement contributions, change careers, work part time, or prioritize other goals like paying down a mortgage or funding a child’s education. Coast FIRE addresses retirement funding — not current living expenses. You still need earned income or other resources to cover today’s bills. Think of it as retirement savings being “coasting” toward the destination while you focus cash flow elsewhere.

The FIRE calculator shows the full independence timeline if you continue contributing, which helps compare coasting against staying aggressive.

Assumptions, margin, and uncertainty

Returns do not arrive smoothly. Markets deliver sequences of strong and weak years, and future spending is uncertain — especially healthcare before Medicare. A Coast FIRE calculation assumes you earn the assumed real return every year, which no portfolio does in practice. Building margin — continuing some contributions, targeting a later retirement date, or using a conservative return assumption — provides room for error.^[3]

Social Security and pensions may reduce the portfolio target you need at retirement, which lowers the Coast FIRE threshold today.^[4] Revisit the calculation when your balance, target date, or spending assumptions change.

Coast FIRE is not the same as retiring today

Confusing Coast FIRE with full financial independence leads to under-saving for near-term needs. You have reached Coast FIRE only relative to a future retirement date and a set of assumptions — not because you can live off investments now. Use the milestone to make informed trade-offs about career and contribution levels, not as permission to stop all retirement saving without reviewing the math.

The compound interest calculator illustrates how additional contributions accelerate growth even after you pass a Coast FIRE threshold — extra savings buy flexibility, not just a higher balance.