What is a FIRE calculator?
A FIRE (Financial Independence, Retire Early) calculator estimates how much wealth you need to cover future living expenses without active income. It projects inflated retirement expenses and applies common FIRE multiples—20× for Lean FIRE, 25× for standard FIRE, and 50× for FAT FIRE.
Coast FIRE is the amount you need today so that, with no further contributions, your portfolio grows to full FIRE by retirement age—discounted using the assumed inflation rate.
How Coast FIRE is calculated
First, yearly expenses at retirement are estimated by inflating today's annual spend over the years until retirement. FIRE corpus is 25× that future expense. Coast FIRE discounts the FIRE amount back from retirement to your target Coast FIRE age using the same assumed inflation rate.
Coast FIRE = FIRE Amount ÷ (1 + inflation rate)^(Retirement Age − Coast FIRE Age)
Where –
| FIRE Amount | 25× inflated annual expenses at retirement |
|---|---|
| inflation rate | Assumed annual inflation rate as a decimal |
Expense at retirement = Monthly expense × 12 × (1 + inflation)^years to retirement
How to use this FIRE calculator
Enter your current monthly expenses, age, planned retirement age, assumed inflation rate, and the age at which you want to reach Coast FIRE. Results update instantly as you move sliders or edit the number fields.
Use Lean FIRE (20×), standard FIRE (25×), and FAT FIRE (50×) as planning benchmarks—not guarantees. Pair this with an SIP or SWP calculator to estimate how much you need to invest each month to reach your target corpus.
FIRE calculator FAQ
What is Coast FIRE?
Coast FIRE is the corpus you need today so your investments can grow on their own until they reach full FIRE by retirement—without saving another rupee after reaching Coast FIRE. This calculator discounts your FIRE amount back from retirement age using your assumed inflation rate.
Why use 25× for FIRE?
The 25× rule comes from the 4% safe withdrawal rate: if you hold 25 years of annual expenses, withdrawing 4% per year may sustain a long retirement. Lean FIRE uses 20× and FAT FIRE uses 50× for tighter or more comfortable spending buffers.
What is the difference between Lean FIRE, FIRE, and FAT FIRE?
All three use your projected annual expenses at retirement as the base. Lean FIRE is 20× that amount, standard FIRE is 25×, and FAT FIRE is 50×. FAT FIRE allows for more travel, healthcare buffer, or legacy goals; Lean FIRE assumes a frugal lifestyle.
Does this calculator include investment returns for Coast FIRE?
Coast FIRE here is computed by discounting your FIRE corpus from retirement back to your Coast FIRE age using the same assumed inflation rate you enter—not a separate equity return. Expense at retirement is inflated from today's monthly spend using that rate over the years until retirement.