Coast FIRE Calculator

Coast FIRE (Coast Financial Independence, Retire Early) is the point where your current investments are large enough that, if you never contributed another dollar, compound growth alone would carry them to your full FIRE number by your target retirement age. You've 'coasted' over the mountain, you just need to let time and compounding do the rest.

Coast FI Number = (Annual Expenses / Safe Withdrawal Rate) × (1 + inflation)^yearsToRetirement / (1 + return)^yearsToRetirement. In plain English: your full FIRE number at retirement (inflated to future dollars), discounted back to today at your expected return rate. If your portfolio equals this number today, it will compound to your full FIRE target by retirement with no further contributions.

Regular FIRE means your portfolio is large enough that you can retire and live off withdrawals today. Coast FIRE means your portfolio is large enough to reach that point by a future date, even with zero additional savings. Coast FIRE requires far less savings upfront, for a 30-year-old planning to retire at 55, their Coast FI number might be $200,000 while their full FIRE number could be $1.25 million.

Lean FIRE targets a frugal retirement on $25,000-$40,000 per year and requires a smaller nest egg (typically $625k-$1M at a 4% SWR). Fat FIRE targets a comfortable or luxurious lifestyle above $100,000 per year, requiring $2.5M-$4M+. This calculator lets you set your own annual expenses and withdrawal rate to model any FIRE variant.

The safe withdrawal rate (SWR) is the percentage of your portfolio you can withdraw in the first year of retirement, then adjust for inflation annually, with a high probability of not running out of money over a 30-year retirement. The 4% rate comes from the Trinity Study (1998), which analyzed US historical market returns. Many planners now use 3.5% for early or long retirements, or a flexible rate that adjusts with markets.