The Financial Independence Number Formula
The core formula comes from the 4% safe withdrawal rate rule (Bengen, 1994):
Financial Independence Number = Annual Expenses ÷ Safe Withdrawal Rate
Or equivalently: Annual Expenses × (1 / SWR)
At 4% SWR: Annual Expenses × 25
At 3.5% SWR: Annual Expenses × 28.5
Which Multiplier Should You Use?
Safe Withdrawal Rate by Retirement Age
| Retirement Age | Retirement Duration | Recommended SWR | Multiplier |
|---|---|---|---|
| 65+ | 25–30 years | 4.0% | 25× |
| 60–64 | 30–35 years | 3.7–3.8% | 26–27× |
| 55–59 | 35–40 years | 3.5% | 28.5× |
| 50–54 | 40–45 years | 3.3–3.5% | 28.5–30× |
| Under 50 | 45–55 years | 3.0–3.3% | 30–33× |
The 4 Expenses Most People Forget
1. Healthcare Before Medicare
If you retire before 65, you need private health insurance. ACA marketplace plans typically cost $400–$900/month unsubsidized per person. Add $6,000–$12,000/year to your annual expense base for this alone.
2. Taxes on Traditional Account Withdrawals
Withdrawals from a 401(k) or traditional IRA are taxed as ordinary income. If your plan calls for $60,000/year from a traditional 401(k), you may need to withdraw $70,000–$75,000 to net $60,000 after federal and state taxes. Use a Roth account strategically to reduce this drag.
3. Sequence-of-Returns Buffer
Many planners add 10–15% to their calculated financial independence number as a buffer against a bad market in years 1–5 of retirement. At $1.5M, that's an extra $150,000–$225,000.
4. One-Time Large Expenses
Roof replacement ($20,000), car purchase ($30,000), wedding gift ($10,000) — these lump sums don't show up in your monthly budget but drain the portfolio. Budget $5,000–$10,000/year for irregular large expenses.
Your Real Financial Independence Number: A Worked Example
Jane, 40, wants to retire at 52. Current annual spending: $65,000. But let's recalculate honestly:
- Base lifestyle: $65,000
- Healthcare (ACA, age 52–65): +$8,400/year ($700/month)
- Irregular expenses buffer: +$6,000/year
- Tax gross-up (traditional accounts): +$5,000/year estimate
- Real annual expense: $84,400
- At 3.5% SWR (28.5× multiplier): Financial independence number = $2,405,400
Jane's initial estimate was $1,625,000 (25 × $65,000). Her real number is $780,000 higher — a 48% difference.
Financial Independence Numbers by Spending Level (Early Retirement, 3.5% SWR)
| Lifestyle | Base Annual Spend | + Healthcare | Real Annual Need | FI Number |
|---|---|---|---|---|
| Lean early retirement | $30,000 | +$5,000 | $35,000 | $1,000,000 |
| Regular early retirement | $50,000 | +$7,200 | $57,200 | $1,630,000 |
| Comfortable early retirement | $70,000 | +$8,400 | $78,400 | $2,240,000 |
| Fat early retirement | $100,000 | +$10,000 | $110,000 | $3,140,000 |
| Ultra fat early retirement | $150,000 | +$12,000 | $162,000 | $4,629,000 |
Enter your income, spending, and target retirement age. Get your personalized financial independence number, current progress %, and retirement age instantly.
Find My Financial Independence Number →Frequently Asked Questions
Mostly yes — with adjustments. Morningstar's 2024 research suggests 3.7% for new retirees using a standard 30-year horizon. For early retirees (40-50 year horizons), 3.3–3.5% is more conservative. The 4% rule remains an excellent starting point for estimating your FIRE number; just add a 10–15% buffer for safety.
Yes — Social Security reduces the portfolio withdrawals you need, effectively lowering your required FIRE number. If SS pays $2,000/month ($24,000/year) and you need $60,000/year, you only need to fund $36,000/year from your portfolio. That drops your FIRE number from $1.71M to $1.03M. The Should I Quit Now calculator models SS automatically based on your estimated benefit and claim age.
Your financial independence number is the portfolio size that generates enough passive income to cover your expenses indefinitely. Some people use different terms — "FI number", "FIRE number", "retirement number" — but they all refer to the same concept: the portfolio value at which work becomes optional. In practice, the math is identical.
Divide your current invested portfolio by your FIRE number. At 25%, you're a quarter of the way there. At 75%, you're in the home stretch. The Should I Quit Now calculator shows this as a readiness score (0–100) with a breakdown by scenario. Many people find that seeing 62/100 vs. a vague "not there yet" is highly motivating — it turns an abstract goal into a measurable milestone.
Use your projected retirement expenses — which are often different from current expenses in both directions. Many people spend less on commuting, work clothes, and childcare but more on healthcare, travel, and leisure. Start with current spending, add healthcare ($6,000–$12,000/year pre-Medicare), subtract work-related costs (~$5,000–$8,000/year), and add a 10% buffer for the unknown.