Finding the Roth Conversion Sweet Spot: How Much to Convert Each Year

Finding Your Baseline Income Before Any Conversion

Before calculating the conversion amount, you need an accurate picture of your income without the conversion. This baseline determines how much bracket space you have available and how close you are to key thresholds. List every income source that will flow in the conversion year: pension payments, part-time work, Social Security if already collecting, dividends and interest from taxable accounts, rental income, and any other ordinary income. Add them up. This is your pre-conversion ordinary income. For a married couple retired at 63, the baseline might look like: $18,000 from a part-time consulting arrangement, $12,000 in taxable interest and dividends from a brokerage account, and $6,000 in rental income. Total pre-conversion income: $36,000. Subtract the 2026 married standard deduction of $32,200: taxable income before conversion is $3,800. That puts them solidly in the 10% bracket. They have roughly $21,000 of room before hitting the top of the 10% bracket ($24,800 taxable income for married filers), and roughly $97,000 of room before hitting the top of the 12% bracket ($100,800 taxable). But this is before accounting for Social Security, IRMAA, and ACA considerations - all of which change the effective cost of each additional dollar of conversion.

The Three Thresholds That Create Hard Limits

Three specific thresholds define the conversion sweet spot and should be modeled carefully before any conversion is executed. Threshold 1 - Tax bracket boundaries. The 12% bracket for married filers in 2026 tops out at $100,800 of taxable income. The 22% bracket runs from $100,801 to $211,400. For a couple with $36,000 in pre-conversion income and a $32,200 standard deduction, converting up to $97,000 ($100,800 taxable income ceiling minus $3,800 baseline taxable income) keeps the entire conversion in the 12% bracket. Each additional dollar beyond $97,000 is taxed at 22%. The jump from 12% to 22% is not a marginal difference - it is an 83% increase in the rate on those dollars. Threshold 2 - IRMAA triggers. IRMAA uses income from two years prior. A conversion in 2026 affects your 2028 Medicare premiums. The first IRMAA tier for married filers begins at $218,001 of 2026 MAGI. If the couple's pre-conversion MAGI (before Social Security, which is added later in the formula) is $36,000, converting up to $181,999 theoretically stays below the threshold - but Social Security income added to the combined income formula makes the real limit lower. Convert $97,000 and the MAGI is $133,000 - well below IRMAA. Convert $180,000 and it is $216,000 - approaching the cliff. A single dollar over the IRMAA threshold triggers $81.20 per person per month in additional Part B premiums starting two years later. Threshold 3 - Social Security taxation. If collecting Social Security, each dollar of conversion increases combined income, which determines what percentage of Social Security is taxable. The 85% taxation threshold is reached when combined income exceeds $44,000 for married couples. Many retirees already sit above this threshold before any conversion. For those below it, a large conversion can push 85% of Social Security into ordinary income - creating a cascading tax cost beyond the stated bracket rate.

How to Calculate the Conversion Sweet Spot Year by Year

The calculation follows a five-step process. Step one: determine pre-conversion ordinary income from all sources (as above). Step two: determine how much of that income is subject to the Social Security taxation formula (AGI + non-taxable interest + 50% of SS). Step three: identify the ceiling you want to stay below - top of 12% bracket, IRMAA threshold minus a buffer, or below a Social Security taxation threshold. Step four: subtract pre-conversion taxable income from your target ceiling. That difference is your available conversion space. Step five: convert that amount - not a dollar more. Example: Married couple, both 65, collecting $22,000 combined Social Security, with $26,000 in pre-conversion income from a small pension and dividends. Combined income before conversion = $26,000 + $11,000 (50% of $22,000 SS) = $37,000. At $37,000, between $32,000 and $44,000, up to 50% of Social Security is already taxable - $11,000. Pre-conversion AGI = $26,000 + $11,000 SS taxable = $37,000. Taxable income = $37,000 - $32,200 standard deduction = $4,800, in the 10% bracket. Target: fill to the top of the 12% bracket ($100,800 taxable income). Remaining room: $100,800 - $4,800 = $96,000 in conversion space at the 12% rate. But converting $96,000 would increase combined income to $26,000 + $11,000 + $96,000 = $133,000 - well above the $44,000 SS taxation threshold, making 85% of SS ($18,700) taxable instead of $11,000. The extra $7,700 in SS income is taxed at 12%, adding $924 to the bill. That is baked into the analysis - the $96,000 conversion at 12% plus the additional SS taxation is still favorable compared to paying 22%+ on RMDs later.

• Calculate pre-conversion ordinary income from all sources before touching the conversion math
• Check Social Security combined income both before and after the planned conversion amount
• Model IRMAA two years forward - use the conversion year's MAGI to check 2028 Medicare costs
• Find the ceiling that matters most: bracket top, IRMAA threshold, or SS taxation cliff
• Convert to that ceiling minus a $2,000-$5,000 buffer to avoid accidental threshold crossings
• Revisit the calculation every year - income sources and thresholds change annually

When the Sweet Spot Shifts: Coordination With Other Income Events

The sweet spot is not fixed. Several common events shift it dramatically in the year they occur. A home sale with a large capital gain increases MAGI significantly in the sale year. If your home sale generates a $300,000 gain (above the $500,000 married exclusion), the IRMAA two years later is already triggered by the sale. Adding a Roth conversion in the same year doubles the IRMAA problem. Better to skip conversions in a high-income year and convert aggressively the following year when income returns to normal. Starting Social Security changes the combined income calculation permanently. The year Social Security begins is often a good year to make a large final conversion - before the full-year SS benefit is flowing - and then reduce conversion amounts in subsequent years as the SS income uses up more bracket space. A part-time consulting arrangement that generates $30,000 extra in a given year reduces conversion space by the same $30,000. Consider whether the consulting income or the conversion produces better long-term value - sometimes the right answer is to skip the conversion that year and use the bracket space for the consulting income instead. Healthcare is a less common but real consideration for early retirees using ACA marketplace insurance. ACA premium tax credits phase out above 400% of the federal poverty level. A large conversion can eliminate ACA subsidies worth thousands in that year. For early retirees who have not yet reached Medicare, the ACA threshold may be more binding than the IRMAA threshold.

The Long View: What the Sweet Spot Saves Over Time

A disciplined 10-year conversion strategy at the sweet spot - converting $80,000 per year at a blended 15% rate rather than taking RMDs of $80,000 per year later at 22-24% - saves approximately $56,000-$72,000 over 10 years in direct bracket-rate savings alone. Add the reduced Social Security taxation that comes from smaller traditional account balances, the IRMAA savings from lower MAGI in RMD years, and the elimination of RMDs for surviving spouses, and the total benefit of a well-executed conversion strategy at the sweet spot can exceed $200,000 over a 25-year retirement. The opposite - converting too much in a single year and triggering IRMAA plus SS taxation - can add $10,000-$20,000 in net costs in a single year, while only marginally reducing the future RMD burden. Getting the amount right each year is the work that turns an average conversion strategy into an exceptional one.