Coast FIRE Calculator

What the Coast FIRE calculator does

Your Coast FIRE number is the amount you need invested today so that, without saving anything more, compound growth carries it to full financial independence by your chosen retirement age. Enter your current age, retirement age, expected annual spending in retirement, expected real return and safe withdrawal rate, and the calculator shows that figure.

FIRE stands for Financial Independence, Retire Early. Traditional FIRE looks at the total you will eventually need; Coast FIRE asks how much you need now for growth to do the rest.

How it works

Invested money earns returns, those returns earn returns, and over decades a balance can multiply several times without new deposits. The calculator first works out your full FIRE number: annual retirement spending divided by your safe withdrawal rate, so a 4% rate means 25 times your yearly spending. It then discounts that target back to today at your real return over the years until retirement. The result is the smaller sum that, left alone, grows into the full figure on schedule.

The more years until retirement, the smaller the Coast FIRE number, because compounding has longer to work. A modest sum invested in your twenties can grow into a full retirement over three or four decades.

The inputs

• Current age and retirement age: the gap is your growth period, and more years mean a smaller number today.
• Annual spending in retirement: this sets the size of your full FIRE target, so spending less lowers everything.
• Expected real return: growth after inflation. A higher figure shrinks the amount needed now, but optimistic assumptions flatter the result.
• Safe withdrawal rate: a lower rate is more cautious and raises both the full and the Coast number.

Why use a real return

Your spending target is in today's money, so discount it with a return that excludes inflation. With 7% expected growth and 2% inflation, enter about 5%. Using the nominal 7% would understate what you need today.

A worked example

You are 30, plan to retire at 65, and expect to spend 40,000 a year in retirement. At a 4% withdrawal rate, your full FIRE number is 40,000 divided by 0.04, or one million. Discounted over 35 years at a 5% real return, one million divided by 1.05 to the power of 35 is roughly 181,000. If you invest about 181,000 today and add nothing more, ordinary market growth should take it to a million by 65.

Retire at 60 instead and the period shrinks to 30 years, so the Coast number rises. Assume a 3% real return and it climbs sharply. Plan to spend less and everything falls in proportion.

Using the result

Reaching your Coast FIRE number means retirement is, on paper, funded, and from then on what you earn can go to other goals: a home, a career change, more time with family or spending a little more now. Markets do not deliver a smooth annual return, though; some decades disappoint and inflation can run higher than expected. Many people who reach Coast FIRE keep investing for a safety margin, to retire earlier or to afford more later. Compare your current balance with the number to see how close you are.

Coast FIRE versus full FIRE

Full FIRE means you have the whole portfolio and could stop working now. Coast FIRE means retirement is secured but you still need to cover living costs until you retire. Many people reach Coast FIRE years or decades before full FIRE, which shows that the early compounding is already under way.

About This Coast FIRE Calculator

Use this Coast FIRE calculator to get an instant estimate based on the figures you enter. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.