Semi-retirement math: portfolio + part-time income

Semi-retirement (Barista FIRE) asks a cash-flow question: if intentional work income covers part of spending, how large a portfolio do you still need? The formula is short. The life design is not. This guide works the math with transparent examples and shows where to stress it.

Core formula

• Gap spending = max(0, annual expenses − annual work income).
• Barista / semi-retirement number = gap ÷ withdrawal rate.
• If work income ≥ expenses, portfolio need for the gap is $0 under this model — you still may want reserves, and the model ignores job risk.
• Full FIRE number remains expenses ÷ SWR for comparison.

Worked table ($60k spend)

• Work $0 → gap $60k → 4% = $1.5M · 3.5% ≈ $1.71M · 3% = $2.0M (full FIRE).
• Work $20k → gap $40k → 4% = $1.0M · 3.5% ≈ $1.14M · 3% ≈ $1.33M.
• Work $30k → gap $30k → 4% = $750k · 3.5% ≈ $857k · 3% = $1.0M.
• Work $45k → gap $15k → 4% = $375k · 3.5% ≈ $429k · 3% = $500k.

Every $10k of durable work income at 4% SWR reduces the portfolio target by $250k. That leverage is why Barista is popular — and why fragile income assumptions are dangerous.

Barista vs Coast vs full FI

• Full FI: portfolio covers spending; work optional.
• Barista: work covers part of spend now; portfolio covers the rest.
• Coast: work still covers full lifestyle spend; portfolio is sized so contributions can stop while compounding toward full FI by traditional retirement age.
• Same person can Coast first (stop maxing retirement savings) then later Barista (cut hours) — different tools for different stages.

Income is not an annuity

• Hours get cut; gigs dry up; clients churn.
• Benefits may vanish below hour thresholds (see healthcare cliffs guide).
• Self-employment taxes and irregular cash flow differ from W-2 part-time.
• Stress case: re-run with work income −25% and −50%, and with a year of $0 work income (bridge reserve).

Spending often rises with free time

Travel, hobbies, and “I have time now” projects can lift expenses exactly when income falls. Model semi-retirement spend as a separate budget, not last year’s full-time lifestyle with salary deleted.

Practical workflow in RetireFire

• 1. Set true semi-retirement spending (with healthcare).
• 2. Enter expected work income in Barista calculator.
• 3. Toggle SWR 4% / 3.5% / 3%.
• 4. Pin Scenario A (full-time / full FIRE path) vs B (semi-retirement inputs).
• 5. Compare Coast if the real question is “stop aggressive saving” not “cut hours.”
• 6. Keep emergency reserves outside the barista pile.
• 7. Revisit yearly — income and benefits change.

Example story (synthetic)

Alex spends $70k, holds $900k invested, can earn $28k part-time. Gap $42k → at 4% needs $1.05M (short ~$150k); at 3.5% needs ~$1.2M. Full FIRE at 4% is $1.75M. Coast to 65 may already be green while Barista is not — meaning Alex might reduce retirement contributions but not yet cut to part-time without a larger pile or lower spend. Numbers are illustrations, not advice.

FAQ

• Does work income get inflated in the model? Simple tools usually treat it as a constant real amount — edit inputs as your plan changes.
• Should I include employer benefits as income? Better to put full costs in spending and cash pay in income.
• Is semi-retirement safer than full FIRE? Often lower portfolio risk target, higher job and benefits risk — different risk, not free lunch.

Open the Barista FIRE calculator, read Barista vs Coast and healthcare cliffs posts, and see Methodology for formulas. Educational only — not financial, tax, or career advice.