What Are Optimism Bias and the Planning Fallacy, and Why Is My Retirement Math Too Rosy?
Last reviewed: July 2026
The planning fallacy in retirement is the tendency to underestimate how long things take, how much they cost, and how long you'll live, which leaves your savings projections too optimistic. Optimism bias is the close cousin: the belief that bad outcomes happen to other people, not you. Together they make retirement math look rosier than reality, because most people quietly assume average expenses, average markets, and an average lifespan. The fix is to plan for the version of retirement that runs long and costs more than you expect.
Key Takeaways
- The planning fallacy makes people underestimate retirement costs and lifespan, producing savings projections that look safer than they actually are.
- A 65-year-old man has a life expectancy near 84 and a woman near 87, per SSA data.
- Optimism bias leads pre-retirees to assume steady markets and low healthcare costs, both of which rarely hold across a 25-year retirement.
- Planning to the upper edge of your longevity range, not the average, is the single most effective correction.
About the Author: Jeff Judge, CFP®, AEP®, ChFC®, CLU® is Managing Partner of Chesapeake Financial Planners in Forest Hill, Maryland. Jeff's observation after hundreds of plan reviews: almost nobody overestimates how long they'll live, and almost everybody underestimates what the last decade of retirement actually costs. He has been helping families and business owners in Harford County and the Baltimore metro area navigate behavioral biases in financial planning since earning his CFP® certification in 2013, by using Chesapeake Financial Planners’ signature process, the R.U.D.D.E.R. method™.
What Is the Planning Fallacy in Retirement?
The planning fallacy is a cognitive bias first described by psychologists Daniel Kahneman and Amos Tversky. It refers to the consistent human tendency to underestimate the time, cost, and risk of future plans, even when we have direct experience telling us otherwise. In retirement planning, it shows up as projections built on best-case assumptions.
Here's how it plays out. A pre-retiree estimates spending $6,000 a month, assumes a 7% return every year, and plans to live to 85. Each number on its own looks reasonable. Stacked together, they describe a retirement that runs shorter, cheaper, and smoother than most actually do. The error isn't in any single assumption. It's in assuming the favorable version of all of them at once.
Jeff Judge often tells clients that the planning fallacy is dangerous precisely because it feels responsible. You ran the numbers. You used a spreadsheet. But a spreadsheet built on optimistic inputs is just a confident way to be wrong. For more on why the process matters more than the inputs, see Why Does a Financial Planning Process Matter More Than Investment Selection?.
What Is Optimism Bias and How Does It Affect Retirement Math?
Optimism bias is the well-documented tendency to expect better outcomes for yourself than the statistical base rate supports. It's why most drivers rate themselves above average and why smokers underestimate their personal health risk. In retirement planning, optimism bias quietly inflates every projection you build.
It affects three areas the most. First, markets: people assume steady positive returns and forget that a bad sequence early in retirement can do lasting damage. Second, health: pre-retirees routinely assume their current good health will hold, when BLS consumer expenditure data shows healthcare spending rises sharply with age. Third, longevity: almost everyone plans to a lifespan near the average, not above it.
The combined effect of optimism bias and underestimating retirement costs is a plan that works on paper and fails in practice. The correction isn't pessimism. It's realism, anchored to data instead of hope.
Why Do People Underestimate How Long They'll Live?
People underestimate longevity because they anchor to life expectancy at birth rather than life expectancy at 65. Those are very different numbers. According to the Social Security Administration, a man who reaches age 65 has an average life expectancy of about 84, and a woman about 87. And that's the average, which means roughly half live longer.
For a married couple, the math gets more demanding. The chance that at least one spouse lives into their 90s is meaningfully higher than the chance for either individual alone. If you plan to age 85 and one spouse lives to 94, you've left nearly a decade unfunded, and it's the most expensive decade because of healthcare and potential long-term care.
This is why longevity is the assumption Jeff pushes hardest on. In his experience, clients will happily debate investment fees for an hour but plan their entire retirement to a lifespan they have no reason to expect. The Society of Actuaries has documented this longevity underestimation across surveys for years. Planning to the upper edge of your range costs you almost nothing if you're wrong and saves everything if you're right.
How Do You Correct for Optimism Bias in Your Retirement Plan?
You correct for optimism bias by replacing single-point assumptions with ranges and by stress-testing the plan against bad outcomes. Here's the practical approach Jeff uses with clients.
Start by planning to age 95, not 85. Then model a poor sequence of returns in the first five years of retirement, because that's when your portfolio is most vulnerable. Build in healthcare inflation that runs faster than general inflation. And separate your "needs" spending from your "wants" spending, so you know which expenses are flexible if markets disappoint.
This is where a structured process beats a one-time projection. At Chesapeake Financial Planners, the R.U.D.D.E.R. Method™ is Chesapeake Financial Planners' six-step planning process: Review and Recognize, Uncover and Understand, Design and Develop, Discuss and Decide, Execute and Empower, and Reassess and Refine. The "Reassess and Refine" step exists specifically because optimistic assumptions get exposed over time, and a plan that never updates is a plan slowly drifting from reality. For the mechanics of turning assets into income, see What is the best order to withdraw from my 401k, Roth IRA, and taxable accounts in retirement? and How do I coordinate all my retirement income sources to minimize taxes and maximize income?. Jeff Judge notes: "A retirement plan that assumes average returns, average healthcare costs, and an average lifespan is essentially three optimistic bets stacked on top of each other, and we stress-test each one separately before we call the plan solid."
Frequently Asked Questions
What is the planning fallacy in simple terms?
The planning fallacy is the human tendency to underestimate how long something will take, how much it will cost, and what could go wrong, even when past experience says otherwise. In retirement, it means projecting a shorter, cheaper, smoother retirement than the one you're likely to live. The cure is planning for the longer, costlier version.
How is optimism bias different from the planning fallacy?
Optimism bias is the broad belief that good things are more likely to happen to you and bad things less likely, compared to the average person. The planning fallacy is a specific result of that bias applied to plans and projections. Optimism bias is the engine; the planning fallacy is one of the things it drives, especially around cost and time estimates.
How long should I plan for retirement to last?
Plan to at least age 95, and to the upper end of your range if you're married, because at least one spouse often lives longer than either expects. SSA data shows a 65-year-old already averages 84 to 87, and averages mean half exceed them. Planning short is the most common and most expensive retirement mistake.
Why do people underestimate retirement costs?
People underestimate retirement costs because they anchor to current spending and assume it stays flat, when healthcare, long-term care, and inflation push later-life costs higher. BLS data shows healthcare spending climbs with age. Optimism bias adds to this by leading people to assume they personally won't face major medical expenses.
Does optimism bias affect how I invest, not just how I save?
Yes. Optimism bias leads investors to assume steady positive returns and to underestimate the damage a bad market early in retirement can cause. This is called sequence-of-returns risk. A plan built on average returns ignores that the order of returns, not just the average, determines whether your money lasts a full retirement.
What's the single best fix for too-rosy retirement math?
The single best fix is to plan to the upper edge of your longevity and cost ranges rather than the average, then stress-test that plan against a poor sequence of early returns. This costs you little if your worries never materialize and protects you completely if they do. Realism, not optimism, is what makes a plan durable.
Should I just assume the worst for every retirement assumption?
No. Assuming disaster everywhere produces a plan so conservative you sacrifice your present unnecessarily. The goal is calibrated realism: plan longevity high, model one bad market sequence, and budget healthcare above general inflation. Be optimistic about the life you want to live; be conservative about the math that funds it.
If your retirement projections feel reassuring, that's worth a second look. We put together a free guide on building realistic retirement income assumptions that walks through the longevity, cost, and sequence-of-returns adjustments most plans miss. Download it at chesapeakefp.com and pressure-test your own numbers before you rely on them.
Disclosures
The information provided is for educational purposes only and should not be construed as investment advice. Investment strategies should be tailored to individual circumstances, risk tolerance, and goals. Past performance doesn't guarantee future results. Consult with qualified financial professionals regarding your specific situation.
Advisors associated with Chesapeake Financial Planners may be either (1) LPL Financial Registered Representatives offering securities through LPL Financial, Member FINRA and SIPC, and investment advisor representatives offering investment advice through Great Valley Advisor Group; or (2) solely investment advisor representatives offering investment advice through Great Valley Advisor Group and not affiliated with LPL Financial. Great Valley Advisor Group, and Chesapeake Financial Planners are separate entities from LPL Financial.
