Skip to navigationSkip to main contentSkip to right columnADVERTISEMENTVishesh RaisinghaniTue, August 11, 2026 at 1:15 PM GMT+2 6 min readBearFotos/ ShutterstockMoneywise and Yahoo Finance LLC may earn commission or revenue through links in the content below.If you're sitting on a huge pile of retirement assets and considering converting some of it to a Roth account, that's probably a good instinct. Roth conversions, according to Vanguard (1), come with an upfront cost, but allow you to accumulate wealth that can grow tax-free forever. Even better, there are no required minimum distributions pulling you into higher brackets in your 70s.However, this seemingly savvy money move hides a relatively expensive trap.Must ReadJeff Bezos backs a platform that lets anyone invest in rental homes for as little as $100 — 6 ways to build wealth like a landlord without actually being oneJPMorgan still sees gold hitting $5,000/oz by Q4 — and savvy investors are protecting their wealth with a tax-advantaged Gold IRA. Learn more with a free guide from Priority GoldThe tax breaks in Trump's 'big beautiful bill' expire after 2028 — and experts say most people won't act in time. What to do before the window closesIn fact, for affluent families, this trap could eliminate seven-figures in tax-free wealth over decades. Here's the pitfall you need to watch out for.The biggest mistake you can makeHere's the underlying mechanism of a Roth conversion: you pay ordinary income tax on every dollar you convert, but only in the year you convert it. And that's where a lot of otherwise careful savers hand the IRS a six-figure tip.There's a temptation to rip the Band-Aid off and just convert the full amount to pay taxes upfront. The bill might seem worth it to create a large pile of capital that can grow tax-free right away. However, this approach can magnify your tax bill and could also trigger surcharges.Let's take the example of a couple aged 63 planning to retire with a combined $1 million in an IRA and $100,000 of other income. According to Vanguard's online calculator (2), converting this amount to a Roth IRA all at once would result in a $160,000 upfront tax.This huge conversion also has implications for Medicare. As of 2026, the highest tax bracket for income related monthly adjustment amount (IRMAA) for couples filing jointly is $750,000 and $500,000 for individuals, per Medicare (3). This is based on a two-year lookback, so a Roth conversion at age 63 would knock this couple into the highest IRMAA surcharge bracket at age 65.The result is $689.90 for Part B and $91 for Part D, every month for that year. An additional combined cost of $6,936, when accounting for your state paying the $209.90 monthly baseline. Altogether, this couple's Roth conversion bill is nearly $167,000.Terms and Privacy PolicyEU DSA contactPrivacy & Cookie SettingsMore Info