Roth conversion: when does it actually pay off

What a Roth conversion is

You move money from a traditional IRA or 401(k) into a Roth IRA. In the year you convert, the converted amount is taxed as ordinary income— but after that, both growth and withdrawals are tax-free for life. It’s a trade: pay the tax now, and leave the future clear.

Why think about it now

A traditional IRA or 401(k) can’t be deferred forever. RMDs force withdrawals starting at age 73, and that amount gets added to your income and taxed that year. Let the lower-income years right after retirement slip by without converting, and you can end up pushed into a much higher bracket the moment RMDs kick in and hit you all at once.

The core idea: fill the bracket

Convert everything in one big year and your income spikes, pushing you into a higher bracket. Instead, spread conversions across several lower-income years after retirement, converting only up to the top of your current bracket each time, and you can lower your average effective tax rate. The years before RMDs start are the window for this.

Traps people miss

• IRMAA — a conversion that raises your income shows up two years later as a surcharge on Medicare Part B/D premiums. Looking only at the tax bill misses the premium increase.
• The ACA subsidy cliff — if you’re on ACA marketplace coverage in early retirement, a conversion can push your MAGI past a point where your subsidy disappears all at once.
• NIIT (net investment income tax) — the conversion itself isn’t investment income, but if your total income crosses the threshold, a 3.8% tax can get added to your other investment income.

The 5-Year Rule

Each converted amount has its own 5-year clock — withdraw it before that 5 years is up and, if you’re under 59½, a 10% early-withdrawal penalty can apply. Treat converted money as money you can lock away, not money you might need soon.