🔥 FIRE Calculator

Lean, Regular, Fat, and Coast FIRE in one calculator. Set your spending, savings rate, and SWR — see exactly when you reach financial independence.

🔥 FIRE Calculator — Lean, Regular, Fat, and Coast FIRE in one tool. Closed-form math, instant results.

Enter Your Details

Current Investments ($)

Current Age

Annual After-Tax Income ($)

Current Annual Spending ($)

Expected Real Return (%, after inflation)

Safe Withdrawal Rate (%)

FIRE Tier

Your Results

Your FI Number

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Years to FI

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Age at FI

Implied Savings Rate

Coast FI Number (today's age)

Year-by-Year Projection

Year	Age	Year-End Investments	% to FI

How to use this calculator

Takes about 3 minutes.

Enter your current investments and age
Add your annual after-tax income and current spending
Pick a real return assumption (5% is the standard FIRE default)
Choose your safe withdrawal rate (4% by default — Trinity Study)
Pick your FIRE tier: Lean (0.7×), Regular (1.0×), Fat (2.0×), or Coast
Review your FI number, years to FI, and coast number

Try these scenarios

Tap a scenario to load it into the calculator above.

Methodology & Sources

This calculator uses the closed-form FIRE projection: years = ln((FI·r + S) / (PV·r + S)) / ln(1 + r), where PV is current investments, S is annual savings (income − spending), r is the expected real return, and FI is your target number. The FI number itself is derived from your safe withdrawal rate: FI = (spending × tier multiplier) / SWR. Tier multipliers: Lean 0.7×, Regular 1.0×, Fat 2.0×, Coast 1.0× (with separate today-discounted target).

4% rule: Trinity Study (Cooley, Hubbard, Walz) — original safe-withdrawal research.
Modern guidance: Bogleheads Wiki — Safe Withdrawal Rates — practitioner-reviewed SWR discussion for long retirements.

Last verified: May 2026.

Key concepts

FIRE basics. Financial Independence, Retire Early. The core formula: save enough that 4% of your portfolio covers your annual spending. At a 4% Safe Withdrawal Rate, your FI number is annual spending × 25.

The 4% rule's origin. William Bengen's 1994 study found a retiree withdrawing 4% of their starting balance, adjusted for inflation, had a very high success rate over 30-year retirements across all historical US periods. The follow-up Trinity Study (1998) confirmed this. For 50+ year FIRE retirements, many recommend 3.0-3.5% to be safer.

Lean, regular, fat, coast. Lean FIRE = lower-budget life (US$30-50k spending); regular = middle (US$50-100k); fat = comfortable (US$100k+). Coast FIRE = enough invested that compounding alone gets you to regular FIRE by traditional retirement age — you only need to cover current expenses until then.

Sequence-of-returns risk. A bear market in your first decade of retirement does disproportionate damage because you're selling assets at low prices to fund spending. FIRE retirees often hold 2-3 years of expenses in cash / short bonds to ride out drawdowns without selling equities.

What FIRE leaves out. Healthcare (especially pre-Medicare in the US), one-off lumpy expenses (roof, car), and lifestyle inflation. Most FIRE planners add 10-20% to their base spending number to absorb these. The calculator's annual-spending input should reflect a realistic post-retirement number, not your tightest possible budget.

UK retire-at-55 specifics. UK savers targeting age 55 face the additional NMPA rise to 57 in April 2028, which creates a two-year ISA bridge requirement on top of the standard FIRE pot — our retire-at-55 calculator sizes the bridge and the UK-modified 3.5% SWR pot.

Worked example — Regular FIRE from age 36

A 36-year-old US software engineer earns $185,000 gross, takes home around $135,000 after tax and 401(k) deferral, and lives on $72,000 a year — about a 47% savings rate against gross or 53% on take-home minus saved. Current invested net worth across 401(k), Roth IRA, and a taxable brokerage is $310,000. Target spending in retirement is $80,000 in today's dollars (so adding a small lifestyle uplift). They want regular FIRE at a 4% SWR — a number close to the original Trinity Study and FRED long-run real-equity-return data.

FI number is $80,000 × 25 = $2,000,000 in today's dollars. Assume 5% real return on a global equity-heavy portfolio. Each year roughly $63,000 of savings flows in (the gap between $135,000 take-home and $72,000 spending, ignoring small variations). Using the calculator's closed-form formula, the portfolio crosses $2 million in about 14 years — making FI age roughly 50. The Coast FIRE number (just enough today that compounding alone gets to $2m by 65) is around $590,000, so this person crosses Coast FIRE somewhere around age 41-42.

Now lift annual spending by $15,000 a year to absorb pre-Medicare healthcare and a more generous lifestyle. FI number jumps to $2.375 million and the timeline pushes out to roughly 18 years (age 54), because the higher spend both raises the target and reduces annual savings. A $15,000 lifestyle decision in your 30s buys you four extra working years — which is exactly why FIRE practitioners obsess about the spending input rather than the income input.

Common mistakes

Modelling the FI number on today's bare-minimum budget. Most people's spending rises with age — kids, healthcare, parents, hobbies. Planning a 50-year retirement against a 30-year-old's lean budget almost always under-shoots. Add 15-25% to current spending before running the projection, then stress-test the lower number as a backup plan.
Ignoring pre-Medicare healthcare in the US. ACA marketplace premiums for a 50-year-old retiree easily run $900-$1,400 a month in 2026 dollars before subsidies, with deductibles on top. FIRE between 45 and 65 needs $12,000-$18,000 a year explicitly in the spending number for health cover — leave it out and the plan looks fine until you actually quit.
Using 4% for a 50-year retirement. The 4% rule was tested against 30-year horizons. For 40-50 years of withdrawals, most modern analysis (Big ERN's series, Kitces, Bogleheads) suggests 3.25-3.5% to keep failure rates equally low. Plugging 4% into a 50-year horizon overstates the safety margin.
Treating taxable, Roth, and 401(k) as one bucket. A $2m FIRE number that's 90% in a Traditional 401(k) is less spendable than the same $2m spread across taxable brokerage and Roth. Before quitting, build a withdrawal plan that bridges from now to 59½ using taxable accounts plus a Roth conversion ladder.
Underestimating sequence-of-returns risk. A 30% drawdown in the first two years of retirement does roughly twice the damage of the same drawdown ten years in. Hold 2-3 years of expenses in cash / short Treasuries at FI date and refill from equities only when markets are up, rather than selling into a downturn for income.

Frequently Asked Questions

What is FIRE (Financial Independence Retire Early)?

FIRE is a movement built around aggressive saving (typically 50%+ of income) and low-cost index investing to reach financial independence decades before traditional retirement age. The 'retire early' part is optional — many FIRE achievers continue working but on their own terms.

What is the 4% rule?

The 4% rule comes from the 1998 Trinity Study and the earlier Bengen (1994) paper. It found that a portfolio of 50–75% stocks and 25–50% bonds could safely sustain 4% annual withdrawals (inflation-adjusted) over a 30-year retirement with very low failure risk. For longer retirements common in FIRE, many planners use 3.0–3.5% as more conservative.

Lean FIRE vs Fat FIRE — what's the difference?

Lean FIRE means low spending in retirement (typically 0.5–0.7× a normal middle-class lifestyle). Fat FIRE means generous spending (2.0× or more — think $200,000+ a year). Regular FIRE sits in between. The cheaper you live, the smaller your FI number — Lean FIRE on $30,000 a year is $750,000; Fat FIRE on $120,000 a year is $3 million.

What is Coast FIRE?

Coast FIRE means you have enough invested today that, with no further contributions, compound growth alone will get you to a regular FI number by traditional retirement age (e.g. 65). Reach Coast FIRE and you can downshift — work less, change careers, take a sabbatical — knowing the math will catch you.

Is the 4% rule still safe in 2026?

It's debated. Bond yields and equity valuations both affect future safe withdrawal rates. Many FIRE practitioners use a 'guardrails' approach (Guyton-Klinger) or a lower starting rate (3.25–3.5%) for retirements lasting 40+ years. This calculator lets you set the SWR yourself.

USA vs UK vs South Africa: where is FIRE easiest?

USA has the largest FIRE community thanks to high-income tech jobs, Roth IRA + 401(k) tax shelters, and low-cost index investing. UK works well with full ISA usage (£20k/yr tax-free) + workplace pension (pension access at 55–57). South Africa is hardest — higher inflation (5%+), Reserve Bank-imposed offshore investment caps (45% of TFSAs), and only R36k/yr of TFSA room mean South African FIRE typically requires a higher savings rate and broader use of taxable accounts.

What's the most common FIRE mistake?

Targeting Lean FIRE because it sounds achievable, without accounting for lifestyle inflation, healthcare, or wanting kids later. A 30-year-old planning to retire on $30k/year often discovers at 40 that they want more — and recovering five lost years of higher savings rate is brutal. Most FIRE veterans now recommend planning for Regular FIRE with the optional ability to scale down rather than aiming for Lean from day one.

What if equity returns are lower than 5% real over my horizon?

Sequence-of-returns risk hits hardest in the first 5 years of withdrawal — bad returns then can permanently impair the portfolio. Defences: hold 1–3 years of expenses in cash/bonds at FI so you don't sell equities during a drawdown; use a variable withdrawal rule (Guyton-Klinger guardrails) that adjusts spending in down years; or aim for a lower SWR (3.25–3.5%) for a wider safety margin. Re-run the calculator with a 4% real return to stress-test your plan.

I've hit my FI number — what's the actual next step?

Don't quit on Friday. Most successful FIRE practitioners recommend a 6–12 month 'soft retire' transition: reduce hours, take a sabbatical, or test the spending in pre-retirement mode. Confirm health-care coverage (USA: ACA marketplace or COBRA), confirm withdrawal accounts and the tax mechanics, and run a Monte Carlo sim of your plan. The math says you can retire — psychology and logistics decide when you actually do.

FIRE vs traditional retirement — what changes?

Time horizon. A traditional 30-year retirement (65 to 95) has well-established 4% safe-withdrawal data. A 50-year FIRE retirement (40 to 90) has far less historical data and requires lower SWR (3–3.5%) for the same failure probability. Other differences: no Social Security/State Pension/SASSA until later, no employer health insurance, and a longer compounding period for any side income — which is why many FIRE retirees end up Coast-FI'ing or Barista-FI'ing with part-time work.

Written and maintained by James Blanckenberg, Founder & Editor, FinCalcHub.

Last reviewed: 17 May 2026 · See editorial policy