Retirement Planning Guide: How to Calculate Your Financial Independence Number

The 60-Second Answer

How do you calculate your financial independence number?

Take your expected annual spending in retirement, multiply by 25. That's your FI number — the asset base that, withdrawn at roughly 4% per year, has historically lasted 30+ years across most market scenarios. Spending $60K/year? Target $1.5M. Spending $100K/year? Target $2.5M. The wealthy don't aim for a retirement age — they aim for the number, contribute aggressively into tax-advantaged accounts, and stop working when the math says it's safe.

Why This Matters

Retiring at 65 Was Never the Goal

"Retirement at 65" is a 20th-century industrial artifact. The right question is not when can I stop working — it's how much do I need so working becomes optional. Answer that, and your timeline becomes flexible: some people hit it at 45, some at 55, some at 70. The number is the goal; the date is the consequence.

This reframe matters because it puts you in charge of the variable that actually moves the date — your savings rate. Saving 10% of income takes ~50 working years to fund retirement. Saving 25% takes ~30 years. Saving 50% takes ~17 years. The math is absurdly leveraged on this single dial.

Pick the number. Pick the savings rate. The age picks itself.

The Four Levers

The Four Pillars of Retirement Planning

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1. Your FI Number

Annual retirement spending × 25 = target asset base. The 4% rule (Trinity Study) shows this base has historically supported 30+ year retirements. For very early retirements, use 28× (3.5%) to add safety margin.

Quick math: $60K spend → $1.5M FI; $80K → $2M; $120K → $3M; $200K → $5M.

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2. Account Optimization

Order matters more than people realize. Standard order: employer match → high-interest debt → HSA → Roth IRA → 401(k) up to limit → taxable brokerage.

Why: matching is 100% return, debt above 7% beats market expected returns, HSA is triple-tax-free, Roth grows tax-free forever, 401(k) defers tax to lower-bracket retirement.

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3. Social Security Strategy

Social Security is income replacement, not a wealth strategy. For most US workers, it covers ~30–40% of pre-retirement income. The big lever: when you claim. Each year delayed past full retirement age (currently 67) increases the benefit ~8%.

Heuristic: if you can afford to wait, delaying to 70 produces the highest lifetime benefit for those who live past their late 70s.

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4. Healthcare Planning

Healthcare is the most under-budgeted retirement category. Medicare starts at 65 — early retirees need a private bridge. Long-term care insurance is a real consideration past age 60. HSAs are the most tax-efficient way to fund medical costs in retirement.

Estimate: a healthy 65-year-old couple now needs ~$315K saved for medical costs over retirement. Plan for it as a real line item.

Worked Example

Reaching $2M in 25 Years on a $90K Salary

Age 35, target $2M FI by 60. Single income, $90K gross, ~$72K take-home.

• Target spend in retirement: $80K/year. FI number = $2M.

• 401(k): $1,200/month + $400 employer match = $1,600/month → $19,200/year.

• Roth IRA: $7,000/year (current limit).

• HSA: $3,850/year (single coverage), invested not spent.

• Total annual contribution: $30,050. Savings rate ~33% of gross.

• Assumed return: 7% real.

• Projected age 60 value: ~$2.05M. FI hit at 60 with margin.

Median income, no inheritance, no business exit. Just consistent contributions across the right account stack for 25 years. The math is unsentimental — and it works.

Avoid These

Common Retirement Mistakes

• Skipping the employer match — leaving free money on the table

• Cashing out 401(k)s when changing jobs

• Ignoring the HSA — most under-used retirement account

• All-Roth or all-Traditional — usually a mix is better

• Forgetting healthcare costs in the FI number

• Counting Social Security as the whole plan

• Investing retirement money too conservatively in your 30s and 40s

• Investing retirement money too aggressively in your 60s

Frequently Asked Questions

Is the 4% rule still valid in 2026? With reasonable assumptions, yes. The 4% rule has held up across multiple updates of the Trinity Study and Bengen's research. For very early retirees (40s) with 50+ year horizons, 3.25–3.5% is a more conservative starting withdrawal rate.

Should I prioritize Roth or Traditional 401(k)? Mostly depends on your current vs expected retirement tax bracket. Traditional makes sense in high-income years (defer tax now); Roth makes sense in lower-income years and for tax diversification in retirement. Many people benefit from a mix.

What's an HSA and why is it the most powerful retirement account? A Health Savings Account (paired with a high-deductible health plan) is triple-tax-advantaged: deductible going in, tax-free growth, tax-free withdrawals for qualified medical expenses (and after 65, ordinary income for anything). No other US account combines all three.

What if I started saving for retirement late? Three levers: aggressive savings rate (30–50%), longer working horizon, and reduced retirement spending target (which lowers the FI number directly). Late starters need to play all three. There's no single button that fixes a 20-year delay, but the combination still works.

Can I retire on Social Security alone? For most people, no — it covers about 30–40% of pre-retirement income. Could be enough for very low-cost-of-living retirees, but most need substantial savings on top. Treat Social Security as a partial floor, not the plan.

How does FIRE (Financial Independence, Retire Early) differ from regular retirement planning? Same math, more aggressive savings rate, often a stricter spending target. Traditional plan: 15–25% savings, retire ~65. FIRE: 40–70% savings, retire 35–50. The principles are identical; the lever pulled harder is savings rate.

What about the role of bonds in a retirement portfolio? Increase as you near and enter retirement. Common rule: bond percentage = age − 20 (or − 30 for more aggressive investors). At age 30, 0–10% bonds is fine. At 65, 30–50% bonds smooths the ride and protects against sequence-of-returns risk in early retirement.