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Lean, Regular, Fat, Coast — pick your FIRE

Lean, Regular, Fat, Coast — the four FIRE variants, what each one means, the maths behind them, how to set up Lean FIRE step by step, and how to pick the right target for your life stage.
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Quick start

FIRE isn't one thing. There are four flavours and FirePath tracks all of them simultaneously. Pick the one that matches your goal, or track all four as reference points along the same journey.

  • Lean FIRE — retire on the essentials only. Cheapest version of free.
  • Regular FIRE — retire at your current spending level. The default target for most people.
  • Fat FIRE — retire with headroom. Your current spending × 1.5 or 2.
  • Coast FIRE — save enough that you can stop saving and still land at a full FIRE target by retirement age. The most-useful psychological milestone.

Each variant gets its own tab on the FIRE screen. Pick one as your primary target in Settings → Display → Default FIRE Type.


The rest of this guide is for users who want to tune the screen. If you're happy with the defaults, you can stop here — everything below is optional customisation.

Going deeper

The 25× rule

Every FIRE variant derives from the same mathematical anchor: the 4% safe-withdrawal rate from the Trinity Study. Invert 4% and you get 25×: you need a portfolio roughly 25 times your annual expenses to retire on withdrawals alone, with a very high probability of the money outlasting you across most historical 30-year periods.

FirePath uses 4% as the default withdrawal rate (so 25× is the default multiplier). You can adjust to 3.5% or 3% in Settings if you want a more conservative target — each adjustment increases the multiplier (3.5% = ~28×, 3% = ~33×).

Lean FIRE in detail

Include in Lean FIRE toggle on an expense
① Toggle defaults to on for every expense. ② Turn off discretionary categories to shape Lean.

Lean FIRE is the version where you cut spending to the bone and retire on essentials only: rent or mortgage, food, utilities, basic transport, insurance. The idea is that if you needed to retire tomorrow — due to health, caring for family, burnout — you could, at a reduced but sustainable lifestyle.

FirePath computes Lean FIRE by summing only the expenses you've flagged Include in Lean FIRE. Every expense has that toggle, defaulting to on. Turn off the ones you'd cut: dining out, travel, hobby subscriptions, the Spotify family plan, the gym membership you could replace with running. What's left is your Lean spending. Times 25 = your Lean FIRE number.

For most users Lean FIRE lands at 40-60% of Regular FIRE. Reaching Lean FIRE first is a huge de-risker — even if markets tank and you can't hit Regular, you have a floor.

How to set up Lean FIRE, step by step

Lean FIRE tab with computed target
① Lean number = included expenses × 25. ② Progress bar against current portfolio.

Lean FIRE is a premium feature, so the first step is being on Premium. After that, it's a five-minute setup — the hard work is thinking honestly about which expenses you'd actually cut.

  1. Make sure every expense is logged. Go to the Income & Expenses screen and review the Expenses tab. Lean FIRE is only as accurate as the expense list it reads from, so missing categories produce a misleadingly low target. Add any recurring spend you've missed (a forgotten streaming service, quarterly insurance, annual rego).
  2. Set each expense's period correctly. Rent is usually monthly, insurance often yearly, groceries weekly. FirePath normalises periods under the hood — weekly × 52, fortnightly × 26, monthly × 12, yearly × 1 — so the annual Lean total comes out right only if the periods are right.
  3. Walk the expense list and flip the Include in Lean FIRE toggle. Open each expense (tap the row on the Expenses tab), look at the toggle near the bottom of the edit form. On = counts toward Lean; Off = excluded. The mental model: "If I had to retire tomorrow on a tight budget, would I still pay for this?"
    • Keep on: rent / mortgage principal and interest, groceries, utilities, basic transport, health insurance, essential medical.
    • Turn off: dining out, travel, streaming services beyond one, hobby gear, non-essential subscriptions, anything you'd comfortably cut.
    • Judgement calls: car costs if public transport is an option; the higher end of a variable food budget; premium insurance when a basic policy would do. There's no wrong answer — pick the Lean version of you.
  4. Open the FIRE screen and check the Lean tab. The Lean FIRE number now reflects the expenses you kept on, × 25 (or whatever multiplier your safe-withdrawal-rate setting implies). Compare to Regular FIRE on the next tab — Lean should be noticeably smaller, typically 40-60% of Regular.
  5. Sanity-check the number. Does it feel right? Too low probably means you were over-zealous turning things off (you'd actually still pay for a few of them). Too close to Regular means you left too many discretionary items on. Revisit step 3 and adjust — this is iterative.
  6. (Optional) Make Lean your default view. Settings → Display → Default FIRE Type → Lean. The FIRE screen now opens on the Lean tab every time. Useful if Lean is your near-term floor and Regular is the longer-term goal you'll switch focus to later.

Refining over time. Your Lean setup isn't set-and-forget. Every few months — when you add a new recurring expense, or your life circumstances change — revisit the include/exclude toggles. A new baby might push childcare from excluded to included; a paid-off mortgage drops a big item out entirely.

Couple / household tip. If you share finances, walk this list together. The conversation is more valuable than the number — "would we still do Netflix if we were both retired?" surfaces real priorities. FirePath doesn't care who ticked which box; it just sums what's left.

Regular FIRE in detail

Your total annual expenses × 25. Not your salary, not your savings rate — just your actual spending. This is the "retire at my current lifestyle" target and it's what most FIRE-chasers have in mind by default.

Two subtleties. First: expenses fluctuate. FirePath uses what you've currently got entered on the Income & Expenses screen. Keep those figures updated and your Regular FIRE number tracks reality. Second: post-retirement spending is usually lower than pre-retirement — no commute, no work clothes, often lower tax bracket — so 25× current expenses is a slightly conservative target.

Fat FIRE in detail

Your Regular FIRE number times a multiplier — 1.5× by default, configurable in Settings. The idea is a deliberate safety margin: retire not just on current spending but with room to travel more, upgrade, be generous, weather a market downturn without tightening the belt.

Fat is for people who don't want to cut it fine. If reaching Regular FIRE means you'd stop working the same day, Fat gives you 18+ months of buffer years baked into the number. Use 1.5× if you want moderate safety; 2× if you want to truly luxuriate.

Coast FIRE — the underrated one

Coast FIRE is the point where your existing invested portfolio, left alone (no new contributions), will compound up to a full FIRE target by your chosen retirement age. Also known as the "you can stop saving" milestone.

The maths: Coast = Regular FIRE / (1 + r)^n, where r is your real return and n is years until your retirement age. Example: $1.5M Regular FIRE, 25 years to age 60, 5% real return → Coast = $1.5M / (1.05^25) ≈ $443k.

Why it matters: most people who discover FIRE in their 30s hit Coast FIRE well before traditional retirement, often by 35-45. Once you hit Coast, you have options: downshift to part-time, change careers to something meaningful but lower-paying, take a sabbatical, or keep pushing to reach Regular FIRE earlier. The portfolio will get you to full FIRE at 60 either way.

Settings → FIRE lets you set the Coast retirement age (default 60). Setting it higher (65-67) produces a lower Coast number (more time to compound); setting it lower (55) produces a higher one.

Why the numbers are in today's dollars

FirePath's projections use real returns — expected return minus inflation — so every number on the FIRE screen is in today's dollars. A FIRE target of $1.5M means you need enough to fund a lifestyle that costs the same as $1.5M would today, not a million nominal dollars 20 years from now. This avoids the confusing exercise of comparing future dollars to current expenses.

The default assumptions — 7% expected return, 3% inflation — give a 4% real return, a reasonable long-term estimate for a 70/30 equity/bond portfolio. Adjust both in Settings → FIRE Calculator if you want to model a different asset mix or a more (or less) optimistic outlook.

Which variant should you target?

Four FIRE variants side-by-side with progress
① Lean ~50% of Regular. ② Coast well below both. ③ Fat = Regular × 1.5 or 2.

Most users start with Regular as the primary target (Default FIRE Type = Regular) and treat Coast as the reassuring "you can take your foot off the gas" threshold. Lean is the safety floor — a concrete number you could always fall back to.

Fat is for users with specific goals (early retirement at 40, travel-heavy retirement, legacy planning) where the extra margin is worth the extra working years to accumulate.

The real power of tracking all four simultaneously: you see your progress against each, which shifts how you feel about your savings rate. "I'm behind on Regular FIRE" feels different when paired with "but I hit Coast FIRE 18 months ago".

Make it yours — Settings that affect this screen

  • Default FIRE Type — Settings → Display. Which variant opens by default.
  • Lean FIRE Included Expenses — Include-in-Lean-FIRE toggle on each expense on the Add/Edit Expense screen. Shapes which expenses count toward the Lean target.
  • FIRE Assumptions — Settings → FIRE. Real return, inflation, tax, safe-withdrawal rate, Fat multiplier, Coast retirement age.
  • FIRE Cards — Settings → App Lists → FIRE Cards. Hide variants you don't care about to keep the screen focused.

Questions or feedback? Email us at woohoosoftware@gmail.com