Free Coast FIRE Calculator

Coast FIRE Calculator – FinancialAha

A Coast FIRE calculator is a financial planning tool used in the FIRE movement (“Financial Independence, Retire Early”). It helps you determine whether your current investments can grow enough on their own to fund your retirement later — even if you stop contributing today.

“Coast FIRE” means:

• You save and invest aggressively early in life.
• Once you hit your “coast number,” compound growth does the rest.
• After that, you only need to earn enough to cover current living expenses, not retirement savings.

The core Coast FIRE formula is:

$\text{Coast FIRE Number} = \frac{\text{FIRE Number}}{(1+r)^t}$Coast FIRE Number=(1+r)tFIRE Number​

Where:

• $r$r = expected annual investment return
• $t$t = years until retirement

Most calculators first estimate your full FIRE target:

$\text{FIRE Number} = \text{Annual Expenses} \times 25$FIRE Number=Annual Expenses×25

This comes from the common 4% withdrawal rule.

Example:

• Desired retirement spending = $40,000/year
• FIRE target = $1,000,000
• Retirement in 20 years
• Investment return = 7%

The calculator estimates how much you need invested today so that growth alone reaches $1,000,000 by retirement.

Typical inputs include:

• Current age
• Retirement age
• Current investments
• Expected investment return
• Annual retirement spending
• Inflation assumptions
• Safe withdrawal rate (SWR)

People use Coast FIRE calculators to:

• Know when they can reduce saving pressure
• Switch to lower-stress jobs
• Work part-time
• Take career breaks
• Balance life and long-term retirement goals