Simple math, visible assumptions, clear warnings.

Shared conventions

Tax law

The tools apply 2026 federal law. Ordinary-income brackets, the standard deduction, and the 0%, 15%, and 20% long-term capital-gains bands come from IRS Revenue Procedure 2025-32. The standard deduction is $16,100 single, $32,200 married filing jointly, and $24,150 head of household, with the age-65 addition applied only where a tool says it is. The One Big Beautiful Bill Act, signed in July 2025, made the 2017 bracket structure permanent, so there is no 2026 sunset for any tool to model.

Social Security taxation follows the provisional-income formula of IRC §86. Its thresholds — $25,000 and $34,000 single, $32,000 and $44,000 married filing jointly — are fixed in law and never indexed. Required distributions follow SECURE 2.0: they start at 73 for people born 1951 through 1959 and at 75 for people born 1960 or later, sized by the IRS Uniform Lifetime Table. Medicare surcharges use the 2026 IRMAA tiers published by CMS, with the two-year lookback in which one year’s income sets the premiums two years later. Social Security claiming uses SSA’s reduction and delayed-credit factors and its 2026 earnings-test limits.

Thresholds over time

Tools that project years ahead index bracket thresholds and deductions forward by the inflation number you enter, because the law indexes them; the §86 thresholds stay frozen, because the law freezes them. The Roth Conversion Planner indexes its thresholds the same way, the Medicare surcharge thresholds included, and reports its totals in today’s dollars: each year’s figure divided by that year’s inflation, then added up.

Rates

Tools that split money between a growth asset and a safe asset use two anchors. The safe asset earns 3.5% a year, the Treasury-bill anchor. The growth asset earns 10% a year wherever no downturn is modeled: that is the compound annual total return of the S&P 500 from 1928 through 2025, a figure that already contains every crash in the record. When a downturn is placed in the bucket simulator, the growth rate is solved instead, as described below. The Roth Conversion Planner uses the same two rates: each account earns its growth share at the growth rate and the rest at the safe rate. The Social Security tool grows invested checks at a return you choose.

Historical data

Market history comes from the annual dataset Aswath Damodaran maintains at NYU Stern, 1928 through 2025: S&P 500 total return with dividends, 3-month Treasury bills, 10-year Treasury bonds, and the consumer price index. The series were verified against the dataset’s published cumulative values. Retirement Date Roulette runs on it directly, and the 10% growth anchor is taken from it.

Testing

The calculation engines ship with nine Node test suites, 585 checks in all, including hand-computed cases. The Roth Conversion Planner’s suite runs 324 of them, including checks that with no conversion and no Medicare surcharge it matches the Withdrawal Order Sandbox to within a dollar in every year. The shared federal tax module is source-reviewed, with its citations kept next to the data it uses.

Never modeled

No tool models state income tax, apart from the two flat rates the Roth Conversion Planner asks for; the 3.8% net investment income tax; the temporary 2025–2028 senior deduction; ACA premium subsidies; or qualified charitable distributions. IRMAA appears only where a tool says it does. None of the tools prepares a tax return, and none forecasts future tax law.

Tool by tool

Roth Conversion Planner

Two questions in one tool: which years are cheap to convert in and how much a year is worth converting, and what a conversion plan does to the whole household against converting nothing. Inputs are in today’s dollars. The household is run year by year in each year’s own dollars: spending, wages, pension, and Social Security rise with inflation; the brackets, the standard deduction with its age-65 addition (a married couple is assumed to be both 65 or older once you are), the capital-gains bands, and the IRMAA thresholds are indexed; the §86 thresholds stay frozen. Spending is what you spend after tax: the tax, any Medicare surcharge, and any early-withdrawal penalty are worked out on top of it. Each year the required distribution comes out first, each spouse’s share on their own clock; the rest of the year’s cash comes from taxable savings, then the traditional account, then Roth; the conversion takes what the traditional account has left; and the year is solved until the tax and the withdrawals that pay it agree.

The diagnosis finds your cheapest years in the projection with no conversions: the longest run of retirement years in which the first dollar converted costs the least. The cost of converting there is computed exactly, dollar by dollar, as the effective marginal rate on each slice in the lowest-income of those years, so the stretches a bracket table hides appear as steps of their own: while each dollar also makes Social Security taxable, a 10% bracket can cost 18.5% and a 12% bracket 22.2%, and gains pushed out of the 0% band cost the bracket rate plus 15%. The later rate is not forecast. The planner takes three candidates from your own numbers — the rate in the cheapest years, the highest rate reached after them, and the highest rate a surviving spouse reaches filing single — adds any gap between your two state rates, and counts converting as worth it only while today’s rate is below the candidate. Those dollar figures are an upper bound: the later rate comes from the projection with no conversions, and every dollar converted lowers it.

The comparison runs your plan — a fixed amount each year in today’s dollars, a bracket filled each year, or income kept under an IRMAA tier — against converting nothing, with both of you living and, if you set a first-death age, with one of you dying. The survivor is you: from that age you file single, keep the larger Social Security benefit and the pension’s survivor share, and both traditional shares follow your distribution clock, while spending does not change. Each year’s IRMAA surcharge comes from income two years earlier, per person aged 65 or older, and counts as a cost; the first two years have no earlier year in the projection and use their own income, and the appeal someone can file after a life-changing event, such as a spouse’s death, is not modeled. The conversion tax is paid either from outside funds, through the same withdrawals, or by withholding from the conversion, which sends less to Roth and, at 59 or younger, draws the 10% penalty on the withheld part. State tax is two flat rates: one on the taxable conversion, one on required distributions and traditional withdrawals. The planner reports lifetime federal and state tax, any penalties, the IRMAA surcharges, and after-tax wealth at the end, all in today’s dollars. After-tax wealth counts Roth at face value, taxable savings less 15% of the unrealized gain, and leftover traditional money less the tax of drawing it out evenly over ten years on top of the last year’s other income, and less the later state rate.

On request, the planner also scans fixed amounts, from $0 up to the traditional balance or $400,000, whichever is smaller, over the plan’s ages, running the whole household at each, and reports the amount that finishes furthest ahead in each world, or converting nothing if none finishes more than a dollar ahead. It is a scan, not an optimizer: other ages, and the bracket or IRMAA rules, may do better. Not modeled: the temporary senior deduction, itemized deductions, ACA subsidies, NIIT, AMT, qualified charitable distributions, the five-year clocks, capital-gains harvesting beyond the gains realized when taxable savings are sold, state tax beyond the two flat rates, and estate tax.

State Tax on Retirement Income

A reference table, not a calculator: for each state and the District of Columbia, how Social Security, traditional withdrawals and conversions, and Roth withdrawals are taxed, with notes on exclusions. The rates were re-checked on September 24, 2026 against the Tax Foundation’s 2026 state table and the other sources listed on the page. A single representative rate cannot capture graduated brackets, age and income tests, local income taxes, or exclusions that switch off at a threshold, and no tool reads the table: you look up a rate and type it into the planner. Each row is a starting point to confirm with the state’s department of revenue.

Real Marginal Rate Explorer

One tax year under 2026 law. It adds IRA or conversion dollars from zero upward and plots the true federal marginal rate at each point: the Social Security torpedo, with the taxable share of benefits recomputed at every step; realized capital gains pushed from the 0% band into the 15% band; and the bracket edges themselves. IRMAA thresholds are drawn as premium cliffs, not tax, with the two-year lookback. Married statuses assume both spouses are 65 or older where the age addition applies. Not modeled: state tax, NIIT, the senior deduction, ACA subsidy cliffs, qualified charitable distributions, and dependents’ credits.

RMD & IRMAA Horizon

The do-nothing baseline. An IRA left untouched compounds to required-distribution age, 73 or 75 by birth year, and the Uniform Lifetime Table then forces money out every year, stacked on Social Security (through §86) and pension income, with each year marked by the IRMAA tier it lands in. For every year before distributions begin, a table solves the gross conversion that would fill the 12%, 22%, and 24% brackets and the amount that would reach the first IRMAA threshold, counting the extra Social Security each conversion makes taxable. The baseline is deliberately extreme: distributions leave the projection instead of being reinvested, and state tax, NIIT, the senior deduction, spouse age differences, and qualified charitable distributions are left out.

Withdrawal Order Sandbox

Taxable (with its cost basis), traditional, and Roth accounts, drawn down in all six possible orders. Each year spending and income rise with inflation, required distributions come out first, the rest comes from the accounts in the chosen order, and federal tax — ordinary brackets, capital gains stacked on top, Social Security through §86 — is solved together with the withdrawals it depends on. A distribution larger than spending is reinvested in the taxable account. The orders are ranked after final taxes: embedded taxable gains are discounted 15%, and the leftover traditional balance is discounted at a rate the tool computes by paying it out over ten years on top of final-year income. Not modeled: IRMAA, NIIT, state tax, dividend and interest drag inside the taxable account, the senior deduction, ACA subsidies, qualified charitable distributions, the basis step-up at death, spouse age differences, and Roth conversions.

Retirement Bucket Simulator

Three, four, or five buckets carry spending through one downturn you place on the timeline: how far the market drops, how many years it stays down, and the year it starts. The drop lands on each bucket in proportion to its growth share, and the market then holds flat for the length you set; there is no assumed rebound, because the shape of a recovery would be a forecast. Spending can follow the 4% rule with inflation raises, a percentage of the current balance, or a fixed amount, and an optional rule cuts spending while the buffer is low. The buckets are compared with buy-and-hold blends at 30%, 60%, and 85% growth and with a rebalanced 60/40 benchmark, which has its own explainer. There are no taxes, since all assets are treated as one pool, and no Monte Carlo success rate. The refill rules and the growth rate are described in the next section.

Retirement Date Roulette

The simulator’s engine run against history instead of assumptions: every start year since 1928 with enough history to cover the whole plan, which is 1928 through 1996 for the default 30-year plan, using each year’s actual S&P 500 total return, Treasury bill rate, and inflation. Spending rises with each year’s actual inflation, and a year counts as a drawdown when the total-return index sits below its prior peak. Red means the money ran out before the plan-to age, amber that it lasted but finished below the starting balance in nominal dollars, and green that the starting balance survived. It is one history, not a forecast, and it leaves out taxes, fees, Social Security and pensions, and any mid-retirement change in spending.

Social Security Claiming-Age Optimizer

Starts from each spouse’s benefit at full retirement age, typed in from an SSA statement; it does not recompute an earnings record. It applies SSA’s factors — a reduction of 5/9 of 1% a month for the first 36 months before full retirement age and 5/12 of 1% beyond, and delayed credits of 2/3 of 1% a month up to age 70 — along with a simplified spousal top-up and survivor rule, and the 2026 earnings test ($24,480, or $65,160 in the year full retirement age is reached), including the recomputation that returns withheld months. Benefits are taxed through §86 on top of wages and other income. Every combination of claiming ages from 62 to 70 is compared, raw and with the early checks invested at a return you choose. Not modeled: divorced-spouse, children’s, and disability benefits, family maximums, survivor claims before full retirement age, state tax, IRMAA, and changes to Social Security law.

Widow's Penalty Simulator

Runs a married household twice: both spouses alive, and one dying at an age you choose. From the death year the survivor files single, the standard deduction falls from $32,200 plus $3,300 to $16,100 plus $2,050 (2026 figures, indexed), Social Security drops to the survivor benefit you enter, and spending drops to the survivor’s level, while the traditional IRA and its required distributions carry on in full. The tool solves the spending each future can sustain, and a counterfactual that keeps married tax treatment separates the smaller check from the tax penalty. Both spouses are modeled at the same age, and state tax, IRMAA, NIIT, the qualifying-surviving-spouse status, final-year medical deductions, pension survivor elections, and the basis step-up on jointly held assets are left out.

Your Heirs' Tax Bill

A snapshot of a non-spouse inheritance under 2026 law. Taxable accounts step up to market value at death and pass without tax on the gain; a Roth passes tax-free; a traditional IRA is paid out over the ten years the SECURE Act allows, in even tenths stacked on each heir’s own income and filing status. The result is what a dollar in each account is worth to the heirs. Not modeled: federal estate tax, state estate and inheritance taxes, spouse heirs, minor or disabled beneficiaries, heirs’ state income tax, the annual distributions some heirs owe inside the ten years, charitable bequests, and future tax law. Heirs’ incomes are assumed equal and constant.

The Long-Term Care Shock

One representative year of care, paid three ways: from the traditional IRA, the taxable account, or the Roth. Qualified long-term care counts as a medical expense deductible above 7.5% of AGI, replacing the standard deduction when it is larger, and tax, taxable Social Security, and the withdrawal are solved together, because the deduction depends on the income the withdrawal creates. The tool compares the effective rate on IRA dollars in a care year with the same withdrawal in a normal year. It is a steady-state snapshot in today’s dollars that assumes the care is fully qualified, and it leaves out the healthy spouse’s medical costs, other itemized deductions, long-term care insurance, Medicaid, state tax, IRMAA, and account balance limits.

Bucket rules and the calibrated growth rate

Every bucket, the reservoir at the back included, holds a growth share — by default 15% in Bucket 1, 50% in Bucket 2, and 85% in the reservoir — and earns that share at the growth rate and the rest at the safe rate: share × growth + (1 − share) × safe. Each year the withdrawal comes out of Bucket 1, reaching further back only when a bucket is empty; then the front buckets are refilled toward their targets, front to back; then every bucket earns its return.

During a downturn nothing is refilled, not even Bucket 2 into Bucket 1. Bucket 1 pays the bills until it is empty, then Bucket 2, and finally the reservoir: a forced sale at depressed prices, shown rather than smoothed over. After the downturn, no more than the year’s spending plus one catch-up year is sold from the reservoir each year, and the catch-up goes to the front bucket first, so a four-year buffer takes four years to come back. Both rules can be switched off in the simulator to see what each one is worth. Retirement Date Roulette applies the same rules, with the downturn defined by the data: any year in which the S&P 500 total-return index sits below its prior peak.

With no downturn placed, the growth rate is 10%, the long-run figure that already contains every crash. When a downturn is placed, using 10% for the other years would count crashes twice, and using the market’s return between bad years would treat the one placed crash as the only bad patch in the plan. The simulator instead solves for the growth rate r that keeps the whole plan compounding at history’s 10%:

(1 + r)^(N − k) × (1 − drop) = 1.10^N

Here N is the plan length in years, k the number of years the downturn lasts, and drop its depth. At the defaults, a 30-year plan with a 30% drop held for 3 years, r = (1.10^30 ÷ 0.70)^(1/27) − 1 = 12.65%. The simulation then tests the timing and shape of the downturn, not its total damage, and changing the downturn re-solves the rate.

The household .buk file

Every calculator reads and writes the same save file. A .buk file is plain JSON with two parts: a household section holding the facts the tools share, such as ages, filing status, account balances, spending, Social Security, other income, and inflation, and a section for each tool’s own settings. Saving from one tool keeps the other tools’ sections intact, so a single file carries a household across the site. Older .buk files saved by a single tool still open and are converted. The file is written to your own computer and never uploaded; because it holds whatever you entered, treat it like any sensitive financial document.

The same document is also kept in your browser. The household page holds one copy in this browser’s local storage, on this device only, so every tool opens with it; saving a .buk file in any tool updates that copy, and opening a household .buk file replaces it. Nothing in it is sent anywhere, and Forget this household on that page removes it, with every tool’s saved settings.

Sources

Tax figures re-checked September 24, 2026.

• IRS Revenue Procedure 2025-32 for the 2026 brackets, standard deduction, and capital-gains bands.
• IRS Publication 590-A for traditional-to-Roth conversion income and recharacterization context.
• IRS Publication 590-B for IRA distributions, the Uniform Lifetime Table, the 10% additional tax on early distributions, basis, and Form 8606 context.
• IRS RMD FAQs for required minimum distribution rules.
• Centers for Medicare & Medicaid Services for the 2026 Part B and Part D income-related premium tiers.
• Medicare.gov cost information for income-related premium context.
• Social Security Administration for full retirement ages, claiming factors, and the 2026 earnings-test limits.
• NYU Stern, Aswath Damodaran: historical returns on stocks, bonds, and bills for the 1928–2025 market data.

The state tax table lists its own sources on its page.