The most common mistake in early retirement planning is not picking the wrong withdrawal rate — it is calculating the number without adjusting for the variables that actually determine whether you run out of money. The 4% rule gives you a starting point. Sequence of returns, healthcare costs, and spending flexibility determine whether that number survives contact with a real retirement.
This guide walks through the actual calculation and the 2026-specific adjustments that matter.
The 25× rule: where it comes from
The FI number formula is simple: annual spending ÷ withdrawal rate = portfolio needed. At a 4% withdrawal rate, that is annual spending × 25.
The 4% figure comes from the Trinity Study (Cooley, Hubbard, Walz, 1998), which found that a 4% initial withdrawal rate, adjusted for inflation annually, survived 95%+ of 30-year historical periods with a 50/50 stock/bond portfolio. That study has held up remarkably well across subsequent decades.
Example: $60,000/year spend → $60,000 × 25 = $1,500,000 FI number.
2026 adjustments
Higher starting bond yields help. In the near-zero rate era (2012–2022), many researchers argued the 4% rule was too aggressive — bonds were paying almost nothing, so the "bond cushion" was theoretical. In 2026, with 10-year Treasuries at 4.5–5%, the bond side of a balanced portfolio earns real income again. This makes 4% more defensible than it was five years ago.
Sequence of returns is still the killer. The early years of retirement matter most. A 30% market drop in year one is far more damaging than the same drop in year fifteen, because you're selling shares at low prices to fund withdrawals. No rule eliminates this risk — flexibility does.
The 40-year horizon problem. The Trinity Study tested 30-year periods. Early retirees (FI at 35–45) may need 40–50 years. At 4%, historical failure rates tick up meaningfully past 35 years. If you're retiring young, consider 3.5% as your planning rate.
The healthcare wildcard
For retirees before Medicare eligibility at 65, private health insurance is the single largest budget uncertainty. In 2026, individual marketplace plans range from $400/month (high-deductible, healthy 30-year-old) to $2,200/month (comprehensive, 60-year-old). Budget conservatively.
A common approach: bake $1,200–1,500/month per adult into your annual spend estimate, then treat anything lower as a bonus. For a couple, that is $28,800–36,000/year — enough to materially change your FI number.
Comparison: withdrawal rates at a $50K/year spend
| Withdrawal rate |
Portfolio needed ($50K/yr) |
Historical failure rate (30yr) |
Historical failure rate (40yr) |
Notes |
| 4.0% |
$1,250,000 |
~5% |
~10% |
Standard Trinity Study baseline |
| 3.5% |
$1,428,571 |
~2% |
~5% |
Better for 40+ year horizons |
| 3.0% |
$1,666,667 |
~1% |
~2% |
Very conservative; suits ultra-early retirees |
Failure rate = portfolio depleted before end of period in historical backtests.
FIRE variants
Lean FIRE: Sub-$40,000/year spend target. Requires strict lifestyle minimalism. Portfolio target often $750K–1M. High exposure to unexpected expenses.
Fat FIRE: $80,000–150,000+/year spend. Portfolio $2M–4M+. Comfortable margin, often still working part-time by choice.
Coast FIRE: Stop contributing, let existing portfolio grow to FI number by traditional retirement age. Useful for people who want to downshift careers now without full retirement. The calculation: what lump sum, compounded at 6–7% annually, reaches your FI number by 65?
The spending flexibility hedge
The single highest-ROI adjustment to any FIRE plan: build in the ability to reduce spending by 10% in down-market years. Research shows this alone cuts 30-year failure rates roughly in half. If you can cut to $45K/year in a bad year without crisis, your $1,250,000 portfolio acts more like a $1,600,000 one.
Common mistakes to avoid
Using current spending, not retirement spending. Drop commuting costs, work wardrobe, childcare — they often disappear. Add healthcare, travel, hobbies.
Ignoring Social Security. Even modest projected benefits ($12,000–20,000/year) meaningfully lower the portfolio required for later retirement decades. Include a discounted estimate.
Building the number without a sequence-of-returns buffer. Hold 1–2 years of cash or short-term bonds. Avoid selling equities in a major down year.
FAQ
Is 4% still safe in 2026?
Yes, for 30-year retirements. For 40+ year retirements with no spending flexibility, 3.5% is more defensible. With spending flexibility, 4% holds up in most historical scenarios.
How do taxes factor in?
Your FI number should reflect after-tax spending. If withdrawals come from a traditional 401(k), build in the marginal tax rate on withdrawals. If mostly Roth, taxes are already paid.
What if I expect an inheritance or asset sale?
Use a conservative estimate (50–70% of expected value) and treat it as a plan buffer, not a plan centerpiece. Inheritance timing is unpredictable.
Where to go next
For more FIRE planning guidance see the FIRE movement explained in 2026, coast FIRE explained, and how to invest during a recession in 2026.