FireFly

FIRE Calculator

Plug in your savings rate and target spending — find your FIRE number and the years until financial independence.

Current age

Current invested savings

Target annual spending in retirement

Annual savings (post-tax)

Expected real return

Safe withdrawal rate

Your FIRE number

$950,000

Based on a 4% safe withdrawal rate

Years to FIRE: 18.0 years
FIRE age: 48

What you entered

Current savings: $40,000Annual spending target: $38,000Annual savings: $24,000Expected return: 7%/yrWithdrawal rate: 4%

1
Your FIRE number (target nest egg)
$38,000.00 × (100 ÷ 4)= $950,000.00
2
Years to reach it, compounding savings and returns
solve for n: $40,000.00 × (1+r)ⁿ + $24,000.00/yr contributions = $950,000.00, at r = 7%/yr= 18.0 years

Result

FIRE number: $950,000

At your current savings rate and expected return, you'd reach financial independence around age 48. Small increases to your savings rate compound into large reductions in years-to-FIRE.

FIRE number by annual spending and withdrawal rate

Your FIRE number is annual spending divided by the safe withdrawal rate. The last column shows how long it takes to reach the 4% target from $50,000 at age 30, saving half your spending each year and earning 7%.

Annual spending	At 3.5% withdrawal	At 4% withdrawal	At 5% withdrawal	Years to FIRE at 4%
$30,000	$857,143	$750,000	$600,000	19.1
$40,000	$1,142,857	$1,000,000	$800,000	19.8
$50,000	$1,428,571	$1,250,000	$1,000,000	20.3
$60,000	$1,714,286	$1,500,000	$1,200,000	20.6
$80,000	$2,285,714	$2,000,000	$1,600,000	21.0
$100,000	$2,857,143	$2,500,000	$2,000,000	21.2

The 4% column is the familiar 25x annual spending; 3.5% is 28.6x and 5% is 20x, and the spread between them on a $50,000 lifestyle is over $400,000 of required savings. That choice matters more than almost any other input, and lower rates are commonly argued for retirements longer than 30 years. Note how little the years column moves across rows: at a constant savings rate the timeline depends on the proportion of income you save, not the absolute amount, which is why cutting spending helps twice - it lowers the target and raises the savings rate simultaneously. Healthcare before Medicare age, sequence-of-returns risk and tax on withdrawals are all real and none are modelled here.

The 25× rule

Your FIRE number is roughly 25 × your annual spending, based on a 4% safe withdrawal rate. Lowering expenses both raises savings AND lowers the target.

Variants of FIRE

Lean FIRE: minimal spending, retire fast. Fat FIRE: maintain a comfortable lifestyle, save longer. Coast FIRE: save enough early that compounding alone gets you to retirement.

The 4% safe withdrawal rate

The Trinity Study found that withdrawing 4% of your portfolio in year one (adjusted for inflation each year after) has historically survived 30+ years of retirement in 95% of scenarios. A $1 million portfolio supports $40,000/year spending. Some FIRE planners use 3.5% for extra safety on 40–50 year retirements.

Frequently asked questions

What is a FIRE number?

Your FIRE number is the portfolio size needed to cover annual expenses indefinitely. Using the 4% rule: FIRE Number = Annual Spending × 25. If you spend $50,000/year, your FIRE number is $1,250,000. Reduce spending by $10,000 and your target drops by $250,000.

How long does it take to reach FIRE?

It depends almost entirely on your savings rate, not your income. At 50% savings rate: ~17 years. At 70%: ~8.5 years. At 25%: ~32 years. This is because a higher savings rate both builds your portfolio faster AND means you need a smaller portfolio (lower spending = lower FIRE number).

Is the 4% rule still valid?

The original Trinity Study used 1926–1995 data. Updated studies through 2024 show 4% still works for 30-year retirements with a 60/40 portfolio. For 40–50 year early retirements, many FIRE planners use 3.25–3.5% for extra safety margin, or plan to earn some income in early retirement.