COAST FIRE Calculator

Coast FIRE is a milestone within the broader Financial Independence, Retire Early movement. Unlike traditional FIRE — where the goal is to accumulate enough wealth to retire and live off withdrawals immediately — Coast FIRE is about reaching a specific savings threshold early enough that compound growth alone carries your portfolio to full retirement readiness, with zero additional contributions required. Once you cross that threshold, your investments are effectively on autopilot. You are no longer racing to save; you are simply waiting for time and compounding to finish the job.

The foundation of Coast FIRE rests on two interconnected calculations. The first is your FIRE number — the total portfolio value you will need at retirement to sustainably cover your living expenses for the rest of your life. This is derived from your expected annual retirement expenses and your chosen safe withdrawal rate, typically 4% based on the widely referenced Trinity Study:

FIRE Number = Annual Retirement Expenses ÷ Safe Withdrawal Rate

So if you expect to spend $50,000 per year in retirement and use a 4% withdrawal rate, your FIRE number is $1,250,000.

The second calculation works backwards from that FIRE number to determine how much you need invested today — your Coast FIRE number — so that compound growth closes the gap between now and retirement without any further contributions. This uses the present value formula adjusted for inflation:

Coast FIRE Number = FIRE Number ÷ (1 + Real Return Rate) ^ Years to Retirement

The real return rate accounts for the effect of inflation on purchasing power and is calculated as:

Real Return Rate = ((1 + Investment Return Rate) ÷ (1 + Inflation Rate)) − 1

For example, if your FIRE number is $1,250,000, you have 30 years until retirement, your expected investment return is 7%, and inflation is 3%, your real return rate is approximately 3.88%, and your Coast FIRE number works out to roughly $390,000. If you already have $390,000 invested today, you never need to contribute another dollar — that amount will grow to $1,250,000 on its own by retirement.

The Coast FIRE Calculator handles all of this in one place. You enter your current age, target retirement age, current investment portfolio value, expected annual expenses in retirement, expected investment return rate, inflation rate, and safe withdrawal rate. The calculator then outputs your Coast FIRE number, the number of years remaining until you reach it at your current savings pace, your projected retirement portfolio value, and a dynamic chart that plots your portfolio’s growth trajectory alongside the Coast FIRE threshold — so you can see the exact crossover point visually.

To use it, fill in each of the seven input fields with your personal figures and click Calculate COAST FIRE. If your current portfolio already exceeds your Coast number, the results confirm that you have already coasted and no further contributions are needed for retirement. If you have not reached it yet, the tool shows precisely how many years remain and what growth looks like between now and that milestone.

Understanding where you stand relative to your Coast FIRE number matters most when you are facing a decision that involves trading income for something else — accepting a lower-paying role, going part-time, starting a business, taking time off to care for a family member, or simply stepping back from a high-pressure career. Without a concrete number, those decisions feel like financial guesses. With your Coast FIRE number in hand, you know exactly what your portfolio needs to look like before you can make any of those moves without jeopardizing retirement. It also reframes how people think about the savings phase of their financial life — shifting the question from “how much do I need to save every month forever” to “how quickly can I reach the point where I no longer have to.”

This calculator is most valuable for people in their 20s, 30s, and early 40s who are in the active accumulation phase and want to know how much runway they have left before they can ease off. It is equally useful for anyone who has already built a meaningful portfolio and is wondering whether they have quietly crossed the Coast threshold without realizing it.