What goes in
The household, timing, balances, spending, state, and coverage details you provide.
Behind the numbers
A guided setup. A result you can inspect.
Start with the details you know. Retireomics carries them through a monthly projection using the assumptions and selected public rules it documents. This page shows what that process includes - and where it stops.
A small set of inputs. A visible chain of reasoning.
The model begins with the details you already know: household timing, Social Security, balances, spending, state, and coverage. Optional details can refine the result later. The point is not to hide complexity; it is to give you a clear path through it.
What happens
The model carries those details month by month through a retirement projection.
What you can inspect
The assumptions, rules, order of operations, and limits that shape the result.
What to question
The parts that need better records, current rules, or professional discussion.
01What goes in
The starting details the model asks you to provide.
Start with what you know.
Start with the details you already know: timing, Social Security, savings, spending, state, and coverage. Optional fields let you refine the model later.
Household
Birth year (and your spouse's, if you're planning as a couple).
Social Security
Your benefit — from your statement, or a single full-retirement-age estimate.
Balances
Taxable, tax-deferred, and Roth account balances.
Coverage
State of residence and your health insurance or Medicare cost.
You do not need perfect records to begin. An estimate can show you which missing detail is worth checking next.
02What happens
How the model moves from your inputs to a monthly projection.
Then the model does the repetitive work.
Everything below runs on the fields you enter. Nothing here is a separate input you have to fill out. This is what “shows its work” means in the computation, alongside the formulas explained on the Methodology page.
Scale and granularity
129,600
simulated months in one worked example
For a 65-year-old, that is 36 years to age 100, 432 months per trial, across 300 Monte Carlo trials. A younger starting age runs longer; an older one runs shorter.
300 trials, not one line
Each trial uses a fresh random annual return for every year, then carries the full plan through that scenario.
Resolved monthly, in a fixed order
Taxable→Tax-deferred→Roth
Each month checks the three balances, applies an RMD if one is owed, and carries the result into the next month.
Tax and Medicare rules
Federal brackets and capital gains
Ordinary income runs through seven federal brackets, with different thresholds for single filers and married couples. Long-term capital gains from taxable withdrawals are modeled separately.
RMD divisor, changing with age
RMD treatment begins at age 73 or 75 by birth year, under the modeled SECURE 2.0 rule.
Six IRMAA tiers, checked per person
Tier 1 — under $109,000 - $0
Tier 2 — up to $137,000 - $81
Tier 3 — up to $171,000 - $203
Tier 4 — up to $205,000 - $325
Tier 5 — up to $500,000 - $446
Tier 6 — above $500,000 - $487
The displayed tiers use the single-filer thresholds. Couple calculations use the modeled married-filing-jointly thresholds.
Timing and state handling
A one-year lag, on purpose
This year’s income sets next year’s modeled tax and IRMAA bill. The real IRMAA system generally uses a two-year lookback; the model simplifies that timing to one year and states the limitation.
Rules change over time
The modeled age-65 senior deduction phases out above $75,000 of income ($150,000 for a couple) and is scheduled to expire after tax year 2028.
26 states with dedicated handling
- 13 states - curated brackets or rates
- 9 states - no state income tax
- 4 states - retirement income exempt
Other states use the flat-rate fallback you set yourself.
Real dollars throughout
The projection uses today’s-dollar terms as it runs, so the modeled tax brackets stay consistent across the years.
03The rule ledger
A dated snapshot of the engine values shown on this page.
Numbers need a date and a definition.
Engine snapshot reviewed August 7, 2026.
| Monte Carlo trials per run | 300 |
| Simulation granularity | Monthly, current age → age 100 |
| Example: age 65, a full run | 432 mo × 300 trials = 129,600 |
| Federal tax brackets | 7 (single-filer) / 7 (married filing jointly — different thresholds, not doubled) |
| IRMAA surcharge tiers | 6, checked per person, per year |
| States with curated bracket/exemption logic | 26 (13 curated + 9 no-tax + 4 exempt) |
| RMD divisor range | 26.5 (age 73) → 6.4 (age 100) |
| Tax / IRMAA timing | One-year lag, by design |
About 129,600: it is a worked example for a 65-year-old, not a universal constant. Total simulated months change with the number of years remaining to age 100.
Use the numbers as a starting point.
Retireomics is an educational retirement decision model. It is not financial, investment, tax, legal, Social Security, Medicare, insurance, or fiduciary advice. A projection is not a forecast or guarantee. It is a modeled result based on the information you enter and the assumptions documented on this site.
Retireomics uses selected public materials from the IRS, SSA, CMS, and Medicare. It is a private tool, not affiliated with or endorsed by any government agency. Check current rules with the relevant agency and discuss personal decisions with a qualified professional. See the Methodology for the full assumptions and limits.
See the model in context
Inspect the method, then try your own numbers.
Read the assumptions first, or start a guided model run when you are ready.
Read the methodologyStart your plan