Explanation
How the calculations work
The rules, assumptions, and math behind Roth conversions, IRMAA, and projections.
NotTaxAdvice models retirement tax systems using explicit rules, defined inputs, and stated assumptions.
The goal is not to predict outcomes, but to explain how outcomes are produced.
Every calculation follows published tax law and mechanical interactions — not heuristics, optimization tricks, or black-box scoring.
What this system calculates
NotTaxAdvice evaluates how different components of the retirement tax system interact over time, including:
+ Ordinary income and tax brackets
+ Roth conversions and taxable income stacking
+ Medicare IRMAA thresholds
+ Capital gains and their interaction with ordinary income
+ Required minimum distributions (RMDs)
Each component is calculated independently, then combined to show how changes in one area affect the others.
How calculations are structured
Calculations are performed in layers.
Each layer answers a specific question before passing results forward.
At a high level:
+ Income sources are identified and categorized
+ Taxable amounts are determined under current rules
+ Thresholds and cliffs are evaluated
+ Interactions between components are applied
This structure makes it possible to see where a change occurred and why it mattered.
Roth conversions
Roth conversions are modeled as ordinary income in the year they occur.
This means they:
+ Stack on top of other income
+ Consume available room within tax brackets
+ Can trigger higher marginal rates
+ May affect Medicare IRMAA in future years
NotTaxAdvice shows how much room exists before a higher bracket or threshold is crossed — and what happens when it is.
Tax brackets and “room left”
Tax brackets are applied marginally, not as a single blended rate.
NotTaxAdvice calculates:
+ Current bracket position
+ Remaining space within each bracket
+ The tax impact of additional income
This makes it clear why a small change can sometimes have a large effect — and when it does not.
Medicare IRMAA
Medicare IRMAA is calculated using modified adjusted gross income (MAGI) from prior years.
The system:
+ Evaluates IRMAA thresholds explicitly
+ Shows when a threshold is crossed
+ Highlights the resulting premium change
Rather than summarizing IRMAA as a penalty, NotTaxAdvice shows the exact mechanism that causes it.
Capital gains and stacking
Capital gains are modeled separately from ordinary income, then combined where rules require.
The system shows:
+ How gains stack relative to ordinary income
+ When preferential rates apply
+ When gains push income into higher thresholds
This helps explain outcomes that often appear inconsistent in traditional tools.
Required minimum distributions (RMDs)
RMDs are treated as forced ordinary income.
NotTaxAdvice shows how RMDs:
+ Increase taxable income over time
+ Reduce flexibility in later years
+ Interact with Roth conversions and IRMAA
This makes long-term pressure visible before it occurs.
Assumptions and scope
All calculations are performed under explicit assumptions, including:
+ Current federal tax law
+ Static rules unless stated otherwise
+ Deterministic outcomes based on inputs
Assumptions are shown so users can understand the limits of each result.
What this system does not do
NotTaxAdvice does not:
+ Optimize for a single “best” strategy
+ Predict future tax law changes
+ Forecast market returns
+ Replace professional judgment
Those decisions remain human — and contextual.
What this system provides instead
By making calculations transparent, users can:
+ See how results were produced
+ Identify which rule or threshold mattered
+ Understand tradeoffs across years
+ Ask better questions of their advisors
The goal isn’t to give answers.
The goal is to make the system legible.