Only 3 Numbers Really Matter for Retirement — Do You Know Yours?

Deciding whether you are ready to retire can feel overwhelming, but the question ultimately comes down to three concrete numbers. Get a clear handle on all three and the answer becomes much easier to see.

Here is what those numbers are and why each one carries so much weight.

1. Investment account balance

The first number you need to know is your total investment account balance: the combined value of your 401(k), IRA, and any taxable brokerage accounts. These savings will supplement your Social Security income once you stop working, which makes knowing the precise figure essential. Beyond the raw balance, you should also consider the tax-adjusted value of each account. A dollar sitting in a traditional 401(k) will eventually be reduced by income taxes when withdrawn, while money in a Roth IRA comes out entirely tax-free. The two accounts may show the same number on paper, but they are worth different amounts in practice.

Once you know your total balance, a safe withdrawal rate tells you how much annual income those savings can reliably provide. Morningstar’s 2025 retirement income research sets the base-case safe starting withdrawal rate at 3.9% for a portfolio holding 30% to 50% in equities, assuming a 30-year retirement horizon with a 90% probability of success. That figure rose from 3.7% in the prior year’s research, with the improvement driven by better capital markets assumptions across nearly every asset class. For a retiree with $850,000 saved, that 3.9% rate translates to roughly $33,150 in first-year income from savings alone. The research also found that flexible strategies, such as a guardrails spending approach, delaying Social Security, or adding Treasury Inflation-Protected Securities, can push the starting withdrawal rate as high as 5.7% for retirees willing to adjust their spending as market conditions shift.

The classic 4% rule remains a widely cited benchmark, but retirees who want the greatest margin of safety may prefer the slightly more conservative Morningstar figure. Those comfortable making dynamic adjustments in down markets can often stretch their withdrawal rate meaningfully higher.

2. Social Security benefit

The second number is your projected Social Security benefit. This monthly payment stands apart from a portfolio balance because it is guaranteed to last for life and automatically adjusts for inflation each year. For 2026, the Social Security Administration announced a 2.8% cost-of-living adjustment, raising the average retired worker’s monthly benefit from approximately $2,008 to about $2,064. That increase of roughly $56 per month reflects the COLA tied to changes in the Consumer Price Index for Urban Wage Earners and Clerical Workers. Over the last decade, the annual COLA has averaged roughly 3%, so this year’s adjustment tracks close to the long-run pace.

Social Security is designed to replace roughly 40% of pre-retirement income, though the actual share varies by earner. The formula is progressive, so higher earners see a smaller percentage replaced. Timing matters just as much as the formula itself. Claiming benefits before your full retirement age permanently reduces each monthly check, while waiting past full retirement age earns delayed retirement credits worth roughly 8% for every year you hold off, up to age 70. For those expecting a long life, or for married couples trying to maximize the survivor benefit, delaying almost always pays off. Calculating your personal breakeven point for waiting until 70 can clarify whether the larger monthly checks eventually outweigh the years of missed payments.

The size of this benefit directly shapes how much your savings need to provide. You can find your personalized estimate through your online Social Security account, which projects your monthly payment at different claiming ages.

3. Annual expenditures

The third number is your projected annual spending. Your combined income from Social Security and savings must cover everything you plan to spend in retirement, including costs that many people consistently underestimate. Healthcare deserves particular attention. Fidelity’s 2025 Retiree Health Care Cost Estimate puts lifetime medical expenses for a single 65-year-old at $172,500, a figure that climbed more than 4% from the prior year’s estimate of $165,000 and does not include long-term care. For a couple, the comparable estimate reaches $345,000. These numbers make clear that healthcare is not a footnote in a retirement budget; it is one of the largest line items.

Medicare costs add another layer of annual pressure. The 2026 Medicare Part B standard premium is $202.90 per month, an increase of $17.90 from the 2025 rate of $185.00. The annual Part B deductible rose to $283 in 2026, up $26 from the $257 deductible in 2025. Both figures tend to increase each year, reinforcing why healthcare costs require their own dedicated line in any retirement plan.

A practical starting point for setting your retirement spending target is to aim for enough income to replace about 80% of your pre-retirement earnings. Keep in mind that many retirees follow what researchers call a “spending smile” pattern: outlays are highest in the active early years, ease off in the quieter middle stretch, and then climb again as medical costs rise later in life. A budget that reflects this arc gives a more accurate picture than one that assumes flat annual spending throughout retirement.

Once you have all three numbers in hand, the final step is to stress-test them against sequence-of-returns risk. A severe market decline in the first few years of retirement can permanently deplete a portfolio before it has a chance to recover, even if the long-run average return looks acceptable on paper. Retirees who account for that risk alongside their balance, their benefit, and their budget are far better positioned to leave work on their own terms.

Editor’s note: This pass corrected the Fidelity healthcare cost increase from “more than 4.5%” to “more than 4%” per Fidelity’s official 2025 press release, softened the 10-year COLA average from a specific 3.1% to “roughly 3%,” added the 2025 Medicare Part B deductible of $257 for comparison context with the 2026 figure of $283, and noted Morningstar’s finding that flexible withdrawal strategies can push the starting rate as high as 5.7%.

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