FIRE Calculator for Families

The standard "25× your expenses" rule gives a ballpark FIRE number — but it ignores two costs that derail family FIRE plans: unfunded college bills and the healthcare gap between early retirement and Medicare at 65. This calculator builds a family-adjusted FIRE number, shows your Coast FIRE milestone, and calculates exactly how many years you need at your current savings rate.

Why families need a different FIRE number

The 25× rule — pioneered by financial planner William Bengen in 1994 and validated by the Trinity Study — says a portfolio of 25 times your annual spending will last 30 years at a 4% withdrawal rate with high historical success rates.¹² That's still the right foundation. But three factors make the family FIRE number materially higher than the simple formula:

1. College costs can't come from retirement withdrawals

If you retire at 45 with a $2M portfolio and a 10-year-old at home, your 4% withdrawal covers $80,000/year in living expenses — but not the $250,000+ in college costs that will arrive in 8 years. If you haven't fully funded the 529 accounts before FIREing, the portfolio must cover both spending and college. This calculator adds unfunded college costs as a lump sum to your FIRE number, so you know what "fully funded" actually means.

2. Healthcare before Medicare: the largest hidden cost in family FIRE

Medicare begins at 65. Retire at 48 and you face a 17-year healthcare gap. ACA marketplace premiums for a family of four in their late 40s run $15,000–$24,000/year before deductibles depending on plan type, location, and subsidy eligibility (IRMAA-aware income management can dramatically reduce this).³

If you plan to manage your MAGI to stay below the ACA subsidy cliff — typically 400% of the Federal Poverty Level — a fee-only advisor can model the exact income target. Without that management, add the full unsubsidized premium to your annual retirement budget.

3. Social Security is a future income stream, not a current one

If you FIRE at 50, Social Security is still 12+ years away (earliest claiming at 62, optimal around 70 for the surviving spouse). Your portfolio must fully sustain you until SS begins. Once it does, the annual portfolio draw drops — which is why the calculator shows your FIRE number with SS as an offset: it tells you the portfolio needed to sustain you until SS kicks in, then shows how the annual draw falls when it does.

For early-retiring families, the spousal coordination strategy matters even more: one spouse can claim early at 62 to generate income during the gap, while the higher earner delays to 70 to maximize the survivor benefit.

Coast FIRE for families: the "slow down" milestone

Coast FIRE is the balance at which you can stop making new contributions and let compound growth carry your portfolio to your FIRE number by age 65 — without any additional savings. Once you've hit Coast FIRE, you've won even if the savings rate drops to zero (say, during a career break, parental leave, or a lower-income creative phase).

The formula: Coast FIRE = FIRE target ÷ (1 + return)^(65 − current age)

At age 42 targeting a $2.5M FIRE number at 7% annual returns: $2,500,000 ÷ (1.07)^23 = approximately $480,000. Once your investable portfolio hits $480K, compound growth alone gets you to $2.5M by 65 — every dollar you save from there accelerates your FIRE date rather than being required for Coast FIRE.

Coast FIRE is especially useful for dual-income families where one spouse wants to downshift: if you've hit Coast FIRE, one earner can shift to part-time, take a sabbatical, or step back to care for kids or aging parents without derailing retirement.

FIRE accumulation priority stack for families

The order you fill accounts matters — both for reaching FIRE faster and for having the right account types to draw from in early retirement:

1. Employer 401(k) match — always first. Even at FIRE, leaving free money on the table doesn't make math sense. Max the match before anything else.
2. HSA family contribution ($8,750 in 2026 — IRS Notice 2026-05).⁴ The only triple-tax account. In early retirement, HSA investments pay medical expenses tax-free — especially valuable during the healthcare gap years. The HSA strategy guide covers the "stealth IRA" approach where you invest the balance and save receipts.
3. Roth IRA ($7,500/person in 2026 — IRS Rev. Proc. 2025-67). Roth contributions (not earnings) can be withdrawn penalty-free at any age — making Roth accounts the most flexible bridge between FIRE and the 59½ penalty-free window. Above the $252,000 MFJ phase-out, use the backdoor Roth strategy.
4. Full 401(k) contribution ($24,500 in 2026 — IRS Rev. Proc. 2025-32). Pre-tax deferrals reduce current-year income, which is valuable at high earning years. Note: accessing pre-tax 401(k) before 59½ requires either a 72(t) SEPP arrangement or the Roth conversion ladder strategy.
5. 529 accounts to hit college targets (see savings benchmarks by age). Fully funded 529s remove college costs from your FIRE number entirely.
6. Taxable brokerage for any remaining surplus. No contribution limits, no age restrictions on withdrawals — the most flexible early retirement asset. See the taxable investing strategy guide for asset location and tax-loss harvesting.

Early retirement tax planning: the conversion ladder

Most early retirees' portfolios are heavily weighted toward pre-tax accounts (401k, traditional IRA). Withdrawing from these before 59½ incurs a 10% penalty. The Roth conversion ladder solves this: starting 5 years before you need the money, convert pre-tax dollars to Roth IRA. After 5 years, those converted funds are available penalty-free at any age.

Example for a family FIREing at 50: begin converting $50,000/year of traditional 401(k) to Roth starting at age 45. By 50, you have $250,000 in 5-year-seasoned Roth conversion funds available without penalty. Each year you add another $50K conversion, staying within a low income bracket (often 22% MFJ after standard deduction).

The early retirement years between FIRE and Social Security are also the optimal Roth conversion window — income drops, brackets are low, and converting now reduces future RMD pressure. The Roth conversion strategy guide covers the bracket-filling math in detail.

The dual-income FIRE decision: who retires first?

Most families don't FIRE simultaneously. The more common path is partial FIRE: one earner reaches financial independence and stops (or shifts to lower-stress work), while the other continues contributing. The calculator treats household savings as a single number, but strategically there are distinct options:

• Full FIRE: both earners retire when the combined portfolio hits the family FIRE number. Highest safety — the portfolio is fully funded before either person stops.
• Barista FIRE: one earner shifts to part-time or flexible work earning $20K–$50K/year. That income covers $20K–$50K of annual expenses, reducing the required portfolio by $500K–$1.25M at 4%. The remaining earner may continue or also scale back.
• One-earner bridge: the higher earner continues to the full FIRE date; the lower earner steps back (caregiving, creative work, part-time). If Coast FIRE has been hit, this has no mathematical impact on retirement timing.

FIRE and the family balance sheet

The FIRE number lives in your investable portfolio — 401(k), IRA, Roth, HSA, and taxable brokerage. Your home equity and 529 accounts are real wealth but they don't generate retirement income. Don't include them in your progress tracking. (Use the family net worth calculator for the full balance sheet picture.)

A fee-only advisor running a family FIRE plan will model: the Roth conversion ladder, Social Security claiming strategy (especially survivor benefit optimization), healthcare cost management for the ACA gap years, and sequence-of-returns risk for an early retiree with a 40-50 year horizon. The standard 4% rule was designed for a 30-year retirement — longer horizons warrant a more conservative withdrawal rate or a flexible spending strategy.