Retired Couple Faces $6,900 IRMAA Surprise After Routine Portfolio Rebalance

A 68-year-old husband and 67-year-old wife with a $1.8 million portfolio did everything the textbooks say to do. Their 80/20 stock-bond mix had drifted to 90/10 after a strong equity run, so they rebalanced. Because most of their assets sit in a taxable brokerage account, one afternoon of selling produced $175,000 in long-term capital gains. The federal tax on those gains, at preferential 0% and 15% rates, was the part they had planned for. The part they had not planned for arrived two years later in the form of a higher Medicare bill.

Because capital gains flow into modified adjusted gross income (MAGI), both spouses jumped two IRMAA tiers, the income-related surcharge tacked onto Medicare Part B and Part D. Combined, the surprise came to roughly $6,900.

IRMAA operates as a cliff. Cross a threshold by a single dollar and the full surcharge applies to both spouses for the entire year. For 2026, the first joint-filer threshold sits at $218,000 in MAGI, with tier boundaries after that at $274,000, $342,000, $410,000, and $750,000. The standard Part B premium is $202.90 per month, and it climbs to $689.90 per month at the top tier. That is per person.

Picture a baseline MAGI of about $150,000 from Social Security, dividends, and a small pension. Layering $175,000 of realized gains on top pushes joint MAGI into the $274,000 to $342,000 band. The surcharge lands two years later because Medicare uses the two-year lookback on your tax return. For context, the tracking 2027 Social Security COLA is running near 3.1%. An IRMAA hit of this size can wipe out an entire year of that cost-of-living adjustment for both spouses combined. (We mapped IRMAA and the other premium traps retirees keep tripping over in a free Medicare guide here).

The couple got the allocation question right. What tripped them up was where the rebalancing trade happened. Selling appreciated equities inside a taxable account triggers a taxable event. The same trade inside a traditional IRA or Roth IRA avoids it. The trade produces identical portfolio outcomes, but only one of them touches MAGI.

Procedural Fixes Most Retirees Overlook

Rebalancing still needs to happen. Drifting from 80/20 to 90/10 is a real risk that needs addressing. The goal is to rebalance in a way that avoids increasing MAGI. Here are four potential moves, in rough order of impact:

1. Rebalance inside the IRA first. Sell equities and buy bonds within a traditional or Roth IRA. No 1099, no capital gain, no IRMAA exposure.
2. Harvest losses against realized gains. If a taxable-account sale is unavoidable, pair it with losers elsewhere in the taxable account. Realized losses net directly against realized gains, reducing MAGI dollar for dollar.
3. Split large trades across a calendar boundary. Sell half in December and half the following January. That splits the MAGI hit across two tax years, which can keep each year under an IRMAA threshold instead of clearing two tiers in one shot.
4. Redirect the cash flows you already have. Point new dividends, interest, and required minimum distributions (RMDs begin at age 73) toward the underweight asset class. That rebalances the portfolio quietly over 12 to 24 months without a single sale.

What to Do Before the Next Rebalance

First, before touching a taxable account, map every planned trade against the joint MAGI thresholds of $218,000, $274,000, and $342,000. If a rebalance would clear a line, move the trade into an IRA or spread it across two tax years. Rebalance often, rebalance small, and rebalance in the right account.

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