The Short Answer

Your retirement number is approximately 25× your expected annual spending in retirement.

That's it. The whole calculation starts there. Someone who plans to spend $50,000 a year in retirement needs roughly $1.25 million in invested assets. Someone planning to spend $100,000 a year needs roughly $2.5 million. The formula scales directly with your spending.

The "25×" comes from the 4% safe withdrawal rate — the research-backed finding that withdrawing 4% of your portfolio in year one, then adjusting for inflation each year, has historically not depleted a diversified portfolio over a 30-year retirement. 1 ÷ 0.04 = 25. That's where the multiplier comes from.

The rest of this page explains why spending — not income — is the right variable, what factors can push your number higher or lower, how Social Security fits in, and how the calculation changes if you're aiming to retire before 65.

It's About Spending, Not Income

This is the most important thing to understand about retirement math, and the thing most people get wrong. Your income during your working years is largely irrelevant to your retirement number. What matters is your spending.

Two households, both earning $120,000 a year. Household A spends $100,000 a year and saves the rest. Household B spends $60,000 a year and saves the rest. Household A needs $2.5 million to retire. Household B needs $1.5 million — and gets there faster because they're saving more each year.

The frugal household has a double advantage: their portfolio target is smaller and they're building that portfolio faster. This is the mathematical heart of why savings rate is the most powerful variable in retirement planning — it moves both sides of the equation simultaneously. See the savings rate calculator for a direct translation of savings rate into retirement timeline.

This also means that reducing your spending has a more powerful effect than increasing your income by the same amount. Cutting $10,000 in annual spending lowers your retirement target by $250,000 (25×) and increases your annual savings by $10,000 simultaneously. A $10,000 raise only does the second part.

Calculating Your Own Number

Start with a realistic estimate of your annual spending in retirement. A few notes:

Use today's dollars. Estimate what you'd need to live comfortably right now — then apply the 25× rule. Inflation is handled implicitly by the 4% rule (withdrawals are adjusted for inflation each year).

Your expenses in retirement will differ from today's. Commuting, work clothing, and childcare costs typically fall. Travel and healthcare costs often rise. Housing may change if you plan to downsize or pay off your mortgage before retirement. Build your estimate from the actual categories, not as a percentage of current income.

Don't forget healthcare. This is the most commonly underestimated expense. Fidelity estimates the average 65-year-old couple spends roughly $315,000 on healthcare throughout retirement, in today's dollars. For early retirees who need to fund their own coverage before Medicare at 65, it can be substantially higher.

Use the FIRE Dashboard to model your specific situation — it lets you set your expenses, current savings, contribution rate, and target retirement age, then projects when you'll reach your number.

How Social Security Changes the Calculation

Social Security is a significant income source for most retirees — and it substantially reduces how much your portfolio needs to cover. The correct way to account for it: subtract your expected annual Social Security benefit from your annual retirement spending, then apply the 25× rule to the remainder.

Your estimated benefit depends on your earnings history and when you claim. The Social Security Administration's website (ssa.gov) shows your current estimate. Claiming at 62 reduces benefits permanently by up to 30% compared to full retirement age (67 for most people). Delaying to 70 increases benefits by 8% for every year past full retirement age — a guaranteed, inflation-adjusted return that no investment can match.

The break-even age for delaying from 67 to 70 is typically around 80–82. If you have reason to believe you'll live past that (good health, family history), delaying is usually worth it financially. If your health is uncertain, claiming earlier may make more sense.

For early retirees, Social Security is a complicating factor. If you retire at 50, you won't claim for at least 12 years. Your portfolio needs to cover the full gap during that period, and your Social Security benefit may be lower than projected because you stopped contributing to the system early. Factor this in by being conservative with your Social Security estimate and ensuring your portfolio can cover full spending for at least the first decade of retirement.

How Early Retirement Changes the Number

The 4% rule was designed around a 30-year retirement — roughly, retiring at 65 and living to 95. If you retire at 45, you're planning for a 50-year retirement. That changes the math in three ways:

Lower safe withdrawal rate. For a 50-year horizon, researchers generally recommend 3–3.5% rather than 4%, to improve the probability that the portfolio doesn't deplete. At 3.5%, your target is roughly 28.5× annual spending instead of 25×. See the detailed explanation on the 4% rule page.

Healthcare is entirely self-funded until 65. Medicare eligibility starts at 65. Someone retiring at 45 needs to budget for private health insurance for 20 years. On the ACA marketplace, premiums can be substantially subsidized if your taxable income is low — many FIRE retirees deliberately manage their taxable income to maximize ACA subsidies. But this requires planning.

Retirement account access is restricted until 59½. 401(k) and IRA withdrawals before 59½ normally carry a 10% penalty. Early retirees typically bridge this with a taxable brokerage account, Roth contribution withdrawals (contributions, not earnings, can be withdrawn penalty-free at any age), or a Roth conversion ladder. This doesn't change the total you need, but it changes the structure — how much is in which type of account matters.

Despite these complications, early retirement is mathematically achievable for people with high savings rates and modest spending. The FIRE vs. Traditional Retirement page covers the tradeoffs in more depth.

Factors That Can Raise or Lower Your Number

Things that lower your required portfolio:

• Substantial Social Security income (reduces portfolio withdrawal needs)

• A pension or other guaranteed income source

• Lower spending through paid-off mortgage, downsizing, or lifestyle simplification

• Geographic arbitrage — moving to a lower cost-of-living area or country

• Part-time work or variable income that covers even a portion of expenses

Things that raise your required portfolio:

• Early retirement (longer horizon, lower withdrawal rate, more healthcare)

• High expected healthcare costs (family history, chronic conditions)

• Supporting children or other dependents through retirement

• Living in a high cost-of-living area with no plans to move

• Conservative return assumptions or concerns about future market conditions

The 25× rule is a starting point for most people, not a precise prescription. Model your own specific situation — your actual expected spending, your Social Security estimates, your healthcare situation — rather than relying on a generic number.

The Most Common Mistakes

Using income instead of spending as the base. A household that earns $200,000 but spends $80,000 needs a $2M portfolio — not the $5M that "25× income" would imply. Always work from spending.

Underestimating healthcare. The single most common budget gap for retirees. Model it explicitly, not as a footnote.

Forgetting about inflation over a long retirement. $60,000/year in expenses today becomes roughly $108,000/year in 30 years at 2% inflation, and $145,000 at 3% inflation. The 4% rule handles this because withdrawals are inflation-adjusted — but your mental model of "I need $60K a year" will need to update as you age.

Treating the portfolio target as the finish line. Getting to 25× your expenses doesn't mean the work is done. Ongoing management of withdrawals, asset allocation, tax strategy, and Social Security timing all affect how long the money lasts.

Planning for a fixed lifespan. People routinely underestimate how long they'll live. A healthy 65-year-old couple has roughly a 50% chance that one of them lives to 90 and a meaningful chance of reaching 95. Plan for a long retirement — it's the unexpected outcome worth insuring against.