Coast FIRE Calculator

Coast FIRE is the point where your existing investments, left completely untouched, will grow to your full financial independence number by your target retirement age. In this model, once the invested balance reaches the Coast FIRE Number, the projection gets to the full FI number by the target retirement age with no further retirement contributions, while living expenses until then are assumed to come from earned income and compounding carries the balance the rest of the way.

It is a widely discussed early milestone in the FIRE movement because it usually comes long before full FIRE. Many people hit Coast FIRE in their thirties, which frees them to switch to a lower stress job, work part time, or take a career break without derailing their retirement.

It takes two steps. First, your FI number is your expected annual retirement spending divided by your safe withdrawal rate. At a 4% rate that is the familiar 25x rule, so $40,000 of spending implies a $1,000,000 FI number.

Second, that future target is discounted back to today using your expected real return and the number of years until retirement. Written out, the Coast FIRE Number is the FI number divided by (1 + real return) raised to the power of the years remaining, so a $1,000,000 target 35 years away at a 7% real return discounts to about $93,700. The longer the runway and the higher the return, the smaller the amount needed invested today.

In this model the answer is the moment your invested balance reaches your Coast FIRE Number, which is what the calculator reports as your coasting status. Past that point the projection reaches your FI number by your target retirement age on compounding alone, so further retirement contributions raise the ending balance or pull the date forward rather than being required to arrive at all.

Reaching it is a milestone rather than an instruction. Coasting stops the retirement saving, not the earning: current living expenses still have to be covered from income, and any goal that is not retirement, such as a house deposit, an emergency fund or education costs, sits outside this calculation entirely.

All three describe the same destination and differ in what covers your spending on the way there. Full FIRE is the endpoint: the portfolio itself covers annual expenses, which the FIRE Calculator sizes at your FI number. Coast FIRE is the earliest of the three, reached when the portfolio no longer needs contributions, while a normal income still pays the bills.

Barista FIRE sits between them, where part-time or lower-paid work covers part of the spending and the portfolio covers the rest. Lean FIRE and Fat FIRE are not stages at all; they are the same endpoint sized to a lower or higher annual spend.