What this calculator answers

Coast FIRE is the point at which your invested portfolio is large enough that, even if you never contribute another dollar, compound growth alone will get you to a comfortable retirement number by your target age. After hitting Coast FIRE, you only need to earn enough to cover current living expenses; you can stop saving entirely. This tool finds your Coast FIRE number based on your retirement target, current age, target age, and assumed real return.

How the math works

Work backward from your retirement number using compound interest. If you need 1.5 million dollars at age 65 and you are 35 years old with an assumed real return of 6 percent, you need a present-day portfolio that grows at 6 percent for 30 years to reach 1.5 million. The math is: required current portfolio equals retirement number divided by (1 plus return) raised to the power of years remaining. The result is your Coast FIRE number.

When to use it

• You are weighing a career change, a sabbatical, or a switch to lower-paid work and want to know whether your existing portfolio supports it.
• You want to set a concrete savings goal that is shorter and more motivating than 'full retirement.'
• You want to understand the leverage of saving aggressively early in your career versus stretching saving over your whole working life.
• You are planning a partial retirement or part-time work phase and want to know when you can stop accumulating.

Common mistakes

• Using nominal returns instead of real (inflation-adjusted) returns. Inflation eats your future purchasing power; the 7 to 10 percent nominal return you see in headlines becomes 4 to 7 percent real.
• Ignoring sequence-of-returns risk. A few bad market years right after hitting Coast FIRE can push your math off track. Coast FIRE assumes average returns, not best- or worst-case scenarios.
• Forgetting health insurance. Coast FIRE only frees you from saving more; it does not provide income or benefits today. Health insurance is often the binding constraint on early retirement decisions.
• Confusing Coast FIRE with Full FIRE. Coast FIRE lets you stop saving; Full FIRE lets you stop working. They are very different milestones with very different numbers.

A worked example

Your retirement number is 1.5 million dollars (based on 60,000 dollars a year of spending and a 4 percent safe withdrawal rate). You are 35 years old and want to retire at 65. Using a 6 percent real return, your Coast FIRE number is 1.5 million divided by 1.06 raised to the 30th power, or roughly 261,000 dollars. Once your invested assets cross 261,000 dollars, you can stop contributing entirely and (in expected value) still hit 1.5 million by age 65.

Frequently asked questions