Tax Bomb RMD Projection Calculator 2026 β Roth Conversion Strategy
Project decades of RMDs from a large pre-tax IRA/401k. See bracket creep, IRMAA cliff, and total lifetime tax. Compare with Roth conversion strategy to find the optimal annual conversion amount.
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Pre-tax annualized portfolio growth $
Social Security, pension, rental income/yr $
Amount to convert per year before RMDs begin ($0 = no conversion) %
Your marginal rate during conversion years $0
Balance at RMD Start Age
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First Year RMD
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RMD at Age 80
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Est. Lifetime Tax (30yr)
RMD Projection β With vs Without Roth Conversion
How the Tax Bomb Works
A large pre-tax IRA or 401(k) grows tax-deferred for decades. At RMD age (73 or 75), the IRS forces minimum withdrawals based on your remaining life expectancy. As you age, the withdrawal percentage increases β at 80 it's about 5.3%, at 90 about 10%. On a $2M account, that's $106,000 per year at 80, potentially pushing your ordinary income into the 22%β32% bracket even if you don't need the money.
The RMD Formula
RMD = Prior Year-End Balance Γ· IRS Distribution Period (by age)
Age 73: divisor 26.5 (~3.77%) | Age 80: 20.2 (~4.95%)
Age 85: 16.0 (~6.25%) | Age 90: 12.2 (~8.2%)
Roth Conversion Tax = Conversion Amount Γ Current Marginal Rate
Conversion Benefit = Future RMD Tax Avoided β Conversion Tax Paid
Age 73: divisor 26.5 (~3.77%) | Age 80: 20.2 (~4.95%)
Age 85: 16.0 (~6.25%) | Age 90: 12.2 (~8.2%)
Roth Conversion Tax = Conversion Amount Γ Current Marginal Rate
Conversion Benefit = Future RMD Tax Avoided β Conversion Tax Paid
Example
Age 60, $1.5M pre-tax, 7% return, $40K other income, no conversion:
Balance at 73: ~$3.2M | First RMD: ~$121K | Total income: $161K β 22%β24% bracket
Balance at 80: ~$4.1M | RMD: ~$203K | Total income: $243K β 32% bracket
IRMAA likely triggered each year above $106K
With $50K/yr Roth conversion for 13 years:
Balance at 73: reduced by ~$650K in conversions (plus tax) β smaller RMDs
Total tax saved over 30 years: potentially $100Kβ$400K
Balance at 73: ~$3.2M | First RMD: ~$121K | Total income: $161K β 22%β24% bracket
Balance at 80: ~$4.1M | RMD: ~$203K | Total income: $243K β 32% bracket
IRMAA likely triggered each year above $106K
With $50K/yr Roth conversion for 13 years:
Balance at 73: reduced by ~$650K in conversions (plus tax) β smaller RMDs
Total tax saved over 30 years: potentially $100Kβ$400K
Extended
Optimal Roth Conversion Finder & IRMAA Visualization
Find the optimal annual Roth conversion amount and visualize how conversions prevent IRMAA cliff triggers
Find the optimal annual Roth conversion amount and see how conversions impact IRMAA brackets and lifetime tax.
10-Year RMD Projection (with vs without conversion)
| Age | Balance (No Conv.) | RMD (No Conv.) | Balance (With Conv.) | RMD (With Conv.) | Tax Saved |
|---|
IRMAA Bracket Analysis β Single Filer 2026
| MAGI Range | Part B Surcharge/mo | Part D Surcharge/mo | Annual Extra Cost | Your RMD Status |
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Frequently Asked Questions
What is the "tax bomb" in retirement?
The "tax bomb" refers to the situation where a large pre-tax IRA or 401(k) balance forces large Required Minimum Distributions (RMDs) in retirement, pushing the retiree into high tax brackets β potentially higher than the brackets they avoided when contributing. Additionally, large RMDs can trigger IRMAA (Medicare surcharges), cause Social Security benefits to be 85% taxable, and phase out other deductions. The tax bomb often hits retirees who were diligent savers but did not plan for the mandatory distributions.
When do RMDs start and how are they calculated?
Under SECURE Act 2.0, RMDs must begin at age 73 for people who reach age 72 after December 31, 2022, and at age 75 for those born after December 31, 1960. The RMD amount each year equals your pre-tax account balance on December 31 of the prior year divided by the IRS Uniform Lifetime Table distribution period for your age. At age 73, the divisor is approximately 26.5 (about 3.77% of balance). At 80, about 5.34%. At 90, about 11.4%. RMDs grow as a percentage of balance each year.
What is IRMAA and how do RMDs affect it?
IRMAA (Income-Related Monthly Adjustment Amount) adds surcharges to Medicare Part B and Part D premiums based on your MAGI from 2 years prior. In 2026, the base Medicare Part B premium is approximately $185/month. The first IRMAA tier begins at $106,000 (single) / $212,000 (MFJ) and adds ~$70/month. Higher tiers add progressively more, up to ~$450/month extra for the highest earners. Large RMDs can push you into IRMAA tiers even if your spending needs are modest, costing thousands per year in additional Medicare premiums.
How does Roth conversion reduce the tax bomb?
Converting pre-tax IRA or 401(k) money to a Roth account moves it out of the pre-tax balance, reducing future RMDs. You pay ordinary income tax on the converted amount in the year of conversion, but future growth and withdrawals from the Roth are tax-free, and Roth accounts have no RMDs during the owner's lifetime. The optimal strategy is often to convert during low-income years (early retirement, before Social Security) to fill up lower brackets β moving money from future high-rate RMDs to tax-free Roth income.
What is the optimal Roth conversion amount?
The optimal conversion amount depends on: current marginal rate vs expected future RMD rate, years until RMDs begin, expected investment returns, state taxes, IRMAA thresholds, and estate planning goals. Common approaches: (1) fill up the 12% or 22% federal bracket each year; (2) convert up to but not exceeding the IRMAA threshold ($106K single); (3) use a tax advisor to model multi-year conversions. Generally, converting aggressively during low-income years before RMDs begin captures the most value.