He Will Buy TIPS for Inflation Protection. The Principal Increase Can Make More of His Social Security Taxable Long Before Treasury Pays Him the Added Principal

Government bond yields have been rising. That has pulled a 68-year-old retiree toward Treasury Inflation-Protected Securities, better known as TIPS. He puts $500,000 into TIPS he holds directly in a regular taxable brokerage account. He expects the money to keep up with inflation.

TIPS yields have climbed to their highest levels since 2008. The 10-year real yield is now about 2.8%, while the 30-year is above 3.2%. They also pay cash interest. The tax surprise is the inflation adjustment to principal: in a taxable account, the IRS treats that increase as current income even though Treasury keeps the added principal until maturity. For someone collecting Social Security, that timing matters.

How Treasury Protects His Principal

A TIPS coupon rate never changes. Instead, Treasury raises the principal when prices rise and lowers it during deflation, and the interest paid every six months is based on that adjusted principal. At maturity, he gets back whichever is larger: the adjusted principal or the amount he started with.

There’s a hitch, though: the added principal stays inside the bond until maturity. Suppose inflation raises the principal by 4% this year. His balance grows by $20,000 on paper. The IRS taxes that increase in the year it happens, usually reported as original issue discount, on top of the cash coupons. This phantom income means paying tax with no cash in hand to match it.

Where Phantom Income Hits His Social Security

He collects $30,000 a year from Social Security. To isolate the effect of the principal adjustment, assume his pension, TIPS interest and other taxable income already total $25,000. To decide how much of his benefit gets taxed, the IRS looks at provisional income: that $25,000 plus half of his Social Security, or roughly $40,000.

For a single filer, benefits start to become taxable once provisional income passes $25,000. Above $34,000, up to 85% of benefits can be taxed. Those thresholds have never been adjusted for inflation. At his current level, roughly $9,600 of his benefits is taxable.

Add the inflation adjustment. His provisional income rises to about $60,000, and he hits the cap: $25,500, or 85% of his benefits, is now taxable. That paper gain pulls roughly another $15,900 of Social Security onto his return. He reports about $35,900 of new taxable income without receiving a dollar of that principal.

Inflation tightens the squeeze over time. The 2027 cost-of-living adjustment is on track for 3.3%, so his benefit rises while those thresholds stay fixed.

He is protected from paying tax twice on the same money, since each taxable adjustment raises his cost basis in the bond. When Treasury pays the adjusted principal at maturity, the amounts he already reported come back tax-free. The real problem is timing: the tax bill shows up years before the cash does.

Which Account Holds the TIPS Decides the Tax Bill

1. A TIPS fund. Funds pay out the income their bonds earn, inflation adjustments included, so he gets cash toward the tax. Those payouts and share price changes add volatility.
2. A traditional IRA. Holding TIPS here creates no separate tax bill each year. Tax comes when he withdraws money, and those withdrawals count toward provisional income in the withdrawal year.
3. A Roth IRA. Qualified withdrawals avoid federal tax entirely. Converting to a Roth creates taxable conversion income, though, which can raise the tax on his Social Security in the conversion year.
4. Series I savings bonds. He can defer federal tax on the interest until he cashes them in. New I bonds currently pay a combined rate of 4.26% for their first six months, including a 0.90% fixed rate. Purchase limits make them impractical for a position this large.

Inflation Protection Still Carries Price Risk

TIPS protect purchasing power if held to maturity, but their market prices still fall when real yields rise. The 10-year real yield rose from 2.4% to 2.8% in September alone. Selling early after such a move could lock in a loss even while the principal adjusts up. Deflation can also shrink the principal and coupons, though Treasury will never pay back less than the original principal at maturity.

Run the Worksheet Before Writing the Check

Before buying, estimate the cash coupon and a reasonable annual principal adjustment. Run both through the IRS Social Security benefits worksheet. Compare what happens with the TIPS in a taxable account, an IRA, and a fund. The hardest mistake to undo is buying a large taxable position and finding at tax time how it raises taxes on benefits.

Set aside cash to cover the tax on the inflation adjustment. TIPS can protect the purchasing power of his principal. The account holding them determines whether that protection also creates a tax bill years before the protected principal reaches his bank.

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