Getting Inflation Wrong by 1% Can Wreck a 20-Year Retirement Plan

How a 1% difference compounds into a completely different retirement

Say you retire at 65 spending $80,000 a year today. You assume 2 percent annual inflation. A colleague in the same position assumes 3 percent. In year one, the difference is only $800: you budget $81,600 and she budgets $82,400 for the same lifestyle. That is nothing. But compounding is relentless.

By year 10, you expect to spend about $97,500 to maintain your lifestyle. She expects $107,500. The gap has grown to $10,000 per year. By year 20, your budget says $118,900 and hers says $144,300. The same lifestyle in the same year now costs 21 percent more under her assumption than under yours. If actual inflation turned out to be closer to 3 percent, you have been underfunding your spending by $25,000 a year by that point, and your portfolio has been depleting faster than your model ever predicted.

The damage is compounded on the other side too. Higher inflation means the real return on your portfolio shrinks. If your investments earn 6 percent nominally and inflation runs at 3 percent instead of 2 percent, your real return drops from 4 percent to 3 percent. That single percentage point of real return, sustained over 20 years, can reduce the terminal value of a $1.5 million portfolio by several hundred thousand dollars. You are withdrawing more and earning less at the same time.

What inflation does to bonds

Bonds are the part of most retirement portfolios designed to be stable. They are supposed to be the ballast when stocks drop. But bonds have a specific and serious relationship with inflation, and most people who hold them do not fully understand it.

When inflation rises, interest rates typically rise with it. When interest rates rise, existing bond prices fall. If you hold a ten-year Treasury that pays 3.5 percent and new bonds start paying 5 percent, nobody will pay full price for your bond anymore. Its market value drops until the yield matches what the market now offers. A portfolio of intermediate-term bonds can lose 10 to 15 percent of its market value in a single year of rising rates, as happened in 2022. That is not a stock market crash; that is the safe part of the portfolio doing the opposite of what retirees expected.

The second problem with bonds and inflation is more subtle: even if you hold to maturity and collect every coupon payment, the purchasing power of those payments erodes. A $35,000 annual coupon that felt comfortable at 2 percent inflation buys noticeably less at 4 percent inflation by the time the bond matures. Bonds provide nominal certainty but real uncertainty, which is the opposite of what most retirees need over a 20- to 30-year horizon.

None of this means you should not hold bonds. It means your retirement plan should account for the real yield on your fixed income, not just the nominal coupon, and recognize that the bond portion of your portfolio is not inflation-proof.

What inflation does to stocks

Stocks are often described as an inflation hedge, and over very long periods that is roughly true. Companies raise their prices when their costs rise. Revenues grow in nominal terms. Dividends tend to increase over time. Over a 30-year horizon, a diversified equity portfolio has historically outpaced inflation by a meaningful margin.

But there is an important caveat for retirees. The long-run averaging does not help if a bad inflation shock hits in your first few years of retirement. When inflation spikes, the Federal Reserve raises interest rates to slow it down. Higher rates increase the discount rate applied to future corporate earnings, which compresses price-to-earnings multiples and drives stock prices down. You can have a period of high inflation accompanied by falling stock prices, which means both sides of your portfolio are working against you at the same time you are drawing down to pay expenses.

For retirees, the sequence of returns matters at least as much as the average return. A 15 percent stock market decline in year two of retirement, combined with inflation running at 5 percent, can set a trajectory that a portfolio never fully recovers from, even if the next 15 years are fine. Equity is a long-term inflation hedge, not a short-term one.

Tax brackets: the one thing that does adjust

There is some good news buried in all of this. Federal income tax brackets have been indexed to inflation since 1985. The 22 percent bracket for a married couple runs from roughly $94,000 to $201,000 of taxable income in 2026. The IRS adjusts those thresholds each year based on the Chained CPI, so they grow roughly in line with inflation.

This is why a projected $250,000 traditional IRA withdrawal 25 years from now should not be compared against today's tax brackets. At 3 percent inflation for 25 years, the top of the 22 percent bracket will sit at something like $418,000 of taxable income. A $250,000 nominal withdrawal could land comfortably in the 12 percent bracket, depending on deductions. Comparing future nominal income against present-day brackets is one of the most common ways retirement projections generate misleading alarm.

Social Security has a cost-of-living adjustment, but it is not the inflation protection it is often advertised to be. The COLA is tied to the CPI-W, a measure that tracks urban wage earners, not retirees. Retirees spend a much larger share of their income on healthcare, which inflates faster than the general index. Multiple studies have found that the purchasing power of a Social Security benefit erodes steadily over a 20-year retirement, even after all the annual adjustments are applied. In 2023 alone, the CPI-W rose 8.7 percent and the COLA matched it, but retiree healthcare costs rose considerably faster. Relying on Social Security to stay even with actual retiree inflation is not a safe assumption.

Beyond Social Security, the protection is thin in other areas as well. Medicare's IRMAA surcharges are indexed to inflation only loosely and have sometimes lagged. State income taxes often have fixed brackets that do not adjust at all. Property taxes, long-term care costs, and out-of-pocket medical expenses generally grow faster than the overall CPI. The federal income tax brackets adjust. Most of what you actually spend in retirement does not.

Healthcare is the inflation category that can break a plan on its own

Healthcare costs have historically grown at 5 to 6 percent per year, roughly double the general CPI. If you budget $15,000 per year for healthcare at age 65 and assume it grows with general 2.5 percent inflation, your model says you will spend $21,000 at age 75 and $28,000 at age 85. If healthcare inflation actually runs at 5 percent, you will spend $24,000 at age 75 and $39,000 at age 85. The gap at age 85 is $11,000 per year, on one line item alone.

Most retirees also see healthcare costs grow as a share of total spending as they age. The travel and entertainment that consumed $20,000 a year at 68 often winds down by 80. But the medical bills, prescription costs, and potential long-term care expenses grow at the same time. A retirement plan that uses a single blended inflation rate for all spending often underestimates what happens to total expenses in the later years of retirement.

Case study: Margaret and Robert, same savings, very different outcomes

Margaret and Robert both retired at 65 with $1.5 million in a diversified portfolio, no pension, and Social Security starting at 70. Both planned to spend $80,000 a year in today's dollars. Both assumed nominal investment returns of 6 percent. The only difference was their inflation assumption: Margaret used 2 percent, Robert used 3 percent.

In Margaret's model, her real return is 4 percent. Spending grows slowly. Her portfolio supports her comfortably to age 92 before the balance approaches zero. She feels good about the numbers and does not look at them again for several years.

In Robert's model, the real return drops to 3 percent. Spending in year 20 is $144,000 instead of $119,000, because the higher inflation is applied to the same base every year. Portfolio withdrawals have to keep pace with actual costs. His model shows the portfolio lasting to age 86, not 92. Six years of income security, gone, because of a single percentage point of inflation applied each year for 20 years.

Now suppose the true inflation rate over those 20 years turns out to be 3 percent. Margaret built her entire plan around the wrong assumption. She has been withdrawing slightly less than she needed in years 1 through 5, which feels like good news, but she has also been mentally anchored to a plan that is no longer accurate. By age 80 she is spending significantly more than her model projected, and the portfolio has less time to recover. She would have been better served by Robert's more conservative assumption, or by revisiting the numbers every few years and updating her inflation estimate based on what she was actually experiencing.

Why you need to update your numbers regularly, not just once at retirement

A retirement projection is not a document you write once and file away. It is a model of the future based on assumptions that change every year. Inflation runs hotter than expected for a stretch. Your portfolio earns more or less than the historical average in a given decade. Your actual spending turns out to be different from what you planned. Healthcare costs do what they always do and outrun the general index.

The value of coming back to your numbers is not that you are smarter about the future than you were before. It is that you are correcting the model with real data you now have. You know what you actually spent last year. You know what inflation has actually been. You know whether your investments earned what you projected. Every year you update the inputs, you are replacing assumptions with facts, and the projection becomes more accurate. A five-year-old retirement projection built on 2021 assumptions is not guiding anyone's decision correctly.

Sequence-of-returns risk makes this especially important in the first five years of retirement. If markets have dropped and inflation has run high in your early retirement years, the original plan may no longer hold. Identifying that early, while you still have options like spending adjustments, part-time work, or delaying Social Security, matters far more than discovering it at age 80 when the runway is short.

What to do with your inflation assumption right now

The historical average CPI from 1926 through 2024 is roughly 3 percent per year. The Fed targets 2 percent, and from 2010 to 2020 it mostly ran below that. Then 2021 through 2023 showed that the pre-pandemic decade was the outlier, not the baseline.

For a 20-year or longer retirement plan, assuming 2 percent is probably too optimistic. The 10-year TIPS breakeven rate, which reflects what bond markets expect inflation to average, has run between 2.2 and 2.5 percent for most of the past few years. For planning purposes, 2.5 to 3 percent is a reasonable baseline. If you plan to spend heavily on healthcare in your later years, building in a higher rate for that category specifically, 5 percent or more, gives you a more honest picture.

The most useful thing you can do is run your plan at two different inflation rates: your expected rate and something 1 percent higher. If both projections support your spending through your target age, your plan is reasonably robust. If the higher-inflation scenario runs out of money years before the lower one, that gap is a real risk worth addressing now while your options are broad.

Inflation does not announce itself. It works quietly, year after year, in the same direction, and a plan built on slightly wrong inputs drifts further off course with every year that passes. Checking in on your numbers regularly is not busywork. It is the most practical thing a retiree can do.

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