Lean FIRE number: how much do you need? (tables)

The Lean FIRE number is not a secret formula. It is the same portfolio identity as every other FIRE style: divide the annual spending you intend to support from the portfolio by the withdrawal rate you are willing to plan with. What makes it “Lean” is only the size of that spending input.

Formula and multiples

• Lean FIRE number = Lean annual spending ÷ SWR.
• 4% SWR → 25 × spending.
• 3.5% SWR → ≈ 28.57 × spending.
• 3% SWR → ≈ 33.33 × spending.
• RetireFire Lean example preset: $40,000/year → $1.0M at 4%, ≈ $1.14M at 3.5%, ≈ $1.33M at 3%.

Full grid (USD, pre-tax illustration)

• $25k spend: 4% → $625,000 · 3.5% → ≈ $714,000 · 3% → ≈ $833,000
• $30k spend: 4% → $750,000 · 3.5% → ≈ $857,000 · 3% → $1,000,000
• $35k spend: 4% → $875,000 · 3.5% → $1,000,000 · 3% → ≈ $1,167,000
• $40k spend: 4% → $1,000,000 · 3.5% → ≈ $1,143,000 · 3% → ≈ $1,333,000
• $45k spend: 4% → $1,125,000 · 3.5% → ≈ $1,286,000 · 3% → $1,500,000
• $50k spend: 4% → $1,250,000 · 3.5% → ≈ $1,429,000 · 3% → ≈ $1,667,000

Read across a row to see SWR sensitivity. Read down a column to see how housing or healthcare “small” increases cascade into six-figure portfolio changes. A $10k permanent spend increase at 4% is a $250k target increase.

Choosing an SWR for a Lean plan

• 4% is a historical U.S. research conversation starter (Bengen / Trinity-style lineage) — not a warranty for 40–50 year early retirements.
• Many early-retirement planners stress 3–3.5% as a planning band, especially with thin discretionary buffers.
• Lower SWR → higher Lean number → more accumulation or more years working — explicit trade-off.
• Flexibility (cuttable spend, part-time optionality) can matter as much as the point estimate.

Coast and Barista numbers at Lean spend

• Full Lean FIRE: spending ÷ SWR (tables above).
• Coast (constant-return sketch): coast ≈ full Lean FIRE ÷ (1+r)^n, with n = years until traditional retirement age.
• Example: $1.0M Lean target, n = 25, r = 5% real → coast ≈ $295k; at 4% real → coast ≈ $375k.
• Barista: gap = max(0, Lean spend − work income); barista number = gap ÷ SWR. $40k spend − $15k work → $25k gap → $625k at 4%.

Workflow in the FIRE Number calculator

• Enter your all-in annual spend (not “hope spend”).
• Set SWR to 4%, then re-run at 3.5% and 3%.
• Use Lean preset only if you need a starting stub — overwrite it.
• Export CSV or copy share URL so the number is reproducible.
• Cross-check Years, Coast, and Barista under the same assumptions.

FAQ

• Is $1M the Lean FIRE number? Only if your spend and SWR imply it (e.g. $40k at 4%).
• Do I include taxes in spending? Be consistent: either model gross needs carefully or treat the simple number as pre-tax illustration and stress upward.
• Should partners use one number or two? Model the household cash-flow unit you actually run.

Part of the Lean FIRE pillar series. See Lean FIRE explained, budget systems, and path/savings-rate guides. Educational tables only — not advice. Methodology and disclaimer apply.