Roth Conversion Bracket-Fill Calculator
Find the optimal Roth conversion amount that fills your target tax bracket without triggering IRMAA surcharges, losing ACA subsidies, or hitting the NIIT threshold.
Your Modified Adjusted Gross Income before any Roth conversion.
Used for ACA subsidy cliff calculation (if applicable).
Why Roth Conversions Need Multi-Constraint Planning
The question “how much should I convert to Roth?” is the most-asked question in retirement tax planning — and the answer is never just about tax brackets. A conversion that looks smart from a bracket perspective can trigger thousands in unexpected costs from Medicare surcharges, lost health insurance subsidies, or investment income surtaxes.
The Four Constraints
1. Federal Tax Bracket
Stay within a target bracket (12%, 22%, 24%) to control the tax rate on the conversion.
2. IRMAA Medicare Surcharge
Avoid crossing an IRMAA tier, which adds $1,000–$6,000+/year to Medicare premiums (2-year lookback).
3. ACA Subsidy Cliff
For under-65 with marketplace insurance: crossing 400% FPL can cost $10,000–$30,000+ in lost subsidies.
4. NIIT Threshold
Crossing $200K/$250K MAGI triggers 3.8% tax on existing investment income.
When to Convert: The Golden Window
The ideal window for Roth conversions is the gap years — after retirement but before Social Security and RMDs begin. During these years, your income is typically at its lowest, giving you maximum room in low tax brackets. With OBBBA making TCJA rates permanent, the 12% and 22% brackets are particularly attractive for conversions.
Related Retirement Tax Tools
IRMAA Medicare Planner
Deep-dive into IRMAA brackets and see exactly how conversions affect Medicare premiums.
ACA Subsidy Cliff Calculator
Optimize your MAGI to maximize ACA health insurance subsidies.
SS Tax Torpedo
See how conversions after Social Security starts affect effective marginal rates.
NIIT Calculator
Calculate your 3.8% surtax exposure and how conversions affect it.