Coast FIRE Calculator

Coast FIRE is one of the most liberating milestones in modern financial planning. Unlike traditional FIRE, which requires building a massive nest egg sufficient to fund full retirement immediately, Coast FIRE identifies the exact point where your existing investments will grow to your full retirement goal through compound interest alone—without you ever having to contribute another dollar of earned income toward retirement.

The mathematical formulation of Coast FIRE leverages the time value of money via the present value equation: Coast Target = Total FIRE Number ÷ (1 + r)ⁿ, where r is the expected real (inflation-adjusted) annual return and n is the number of years remaining until your target traditional retirement age. Because compound interest scales exponentially over multi-decade horizons, reaching this milestone in your twenties or early thirties requires a surprisingly modest portfolio.

For example, if you require a $1,250,000 portfolio at age 65 to fund a comfortable retirement, and you achieve a 7% real compound growth rate, a 25-year-old only needs approximately $83,400 invested today to Coast. Once that $83,400 is locked into index funds, compound interest will naturally balloon the balance to the full $1.25 million by age 65 without an additional cent in contributions.

Achieving Coast FIRE unlocks extraordinary career flexibility. Once your future retirement is mathematically guaranteed, you no longer need a high-stress corporate job to maintain a 50% savings rate. You can switch to part-time consulting, take mini-retirements, launch an entrepreneurial passion project, or work for a non-profit, since you only need to generate enough income to cover your day-to-day living expenses.