FIRE Calculator — Your FI Number and Years to Financial Independence

Most FIRE calculators use a flat 4% safe withdrawal rate regardless of how long your retirement actually lasts. A 52-year-old retiring today faces a 38-year horizon — not 30 years — and the research is clear that the safe rate drops for longer periods. This calculator picks the rate that matches your horizon, shows a spending sensitivity table, and flags the three practical issues most early retirees face: pre-59½ account access, healthcare before Medicare, and the ACA subsidy cliff.

Why your retirement horizon changes your FI number

The 4% rule comes from William Bengen's 1994 research on 30-year retirement periods. A retiree at 52 isn't planning a 30-year retirement — they're planning a 38-year one, or longer if they model to age 95. At longer horizons, historical data supports lower initial withdrawal rates:¹

The difference is not trivial. Applying a 4% rate to a planned retirement at 45 underestimates your FI number by about 8%. That's roughly $200K on an $80K spending plan — which could be 3–4 years of additional work, or a meaningful sequence-of-returns buffer you simply left out of the model.

The three early retirement complications this calculator flags

1. Pre-59½ account access

Most retirement savings are in 401(k)s and IRAs with a 10% penalty for withdrawals before age 59½. Early retirees need a bridge strategy. The most common options:

• Rule of 55: Penalty-free 401(k) access if you separate from your employer at age 55 or older. Only applies to the plan at the job you left at 55+. Doesn't help if you retire at 52.
• Roth conversion ladder: Convert traditional IRA money to Roth each year during early retirement. After 5 years of seasoning per conversion, the principal can be withdrawn tax-free and penalty-free. Requires 5 years of bridge assets (taxable brokerage or Roth contributions).
• 72(t) SEPP: Substantially equal periodic payments allow penalty-free IRA withdrawals at any age — but you're locked in for 5 years or until 59½, whichever is longer.
• Taxable brokerage: No age restriction, no penalty. Long-term gains taxed at 0% for incomes under $49,450 single/$98,900 MFJ in 2026.²

2. Healthcare before Medicare at 65

For most early retirees, this is the most expensive line item that doesn't appear in a standard FI calculation. An unsubsidized ACA silver plan for a 58-year-old runs $900–$1,500/month — $10,800–$18,000/year — before out-of-pocket costs. A 52-year-old retiring today faces 13 years of private healthcare costs before Medicare eligibility. That's a significant budget item, and it interacts directly with Roth conversion planning (conversions count as MAGI income).

3. ACA subsidy cliff

ACA premium tax credits phase out as income climbs, and a hard cliff exists at 400% of the federal poverty level — $63,840 for a single person in 2026.³ An early retiree who keeps MAGI below this threshold can receive substantial subsidies ($300–$800/month). One dollar over the cliff creates a benefit cliff that can cost $8,000–$15,000/year in lost subsidies. Managing Roth conversions, capital gains realizations, and other income sources to stay below this threshold is one of the most impactful planning moves an early retiree can make.

What "FI number" actually means in practice

Your FI number is the portfolio size at which you can theoretically sustain indefinite withdrawals at your target spending level — assuming the long-run historical real return of a diversified equity portfolio holds, that you retire into an average sequence of returns (not a 1966 or 2000 sequence), and that spending stays flat in real terms.

None of those assumptions are guaranteed. This is why the FI number is a planning target, not a green light. Most serious early retirement planners run Monte Carlo simulations alongside the simple FI calculation to understand success probability across different market sequences — not just the historical average.

The calculator above gives you the deterministic target. The Monte Carlo simulator gives you the probability distribution around it. The SWR calculator lets you explore the tradeoff between withdrawal rate and portfolio survival across 30–50 year horizons.