Methodology and sources

Who makes Dipperfield

Dipperfield is made and run by WaveApp LLC, 30 N Gould St Ste N, Sheridan, WY 82801. It is calculation software, and nobody at Dipperfield gives tax, legal or investment advice. Dipperfield is not affiliated with Medicare, CMS, the IRS, the Social Security Administration or HealthCare.gov.

To report a figure that looks wrong, write to hi@dipperfield.com with the page, the tax year it shows, the figure and what you expected.

How the numbers are computed

Every figure is arithmetic on your inputs and the published tables listed below. No AI model takes part in any calculation, and the same inputs give the same answer every time. One engine runs the free calculators, the planner and the MCP server. The free calculators and the free planner run in your browser with no account. In the planner, each number opens into the arithmetic behind it and names the table, year and document it came from.

Federal tax follows Form 1040: up to 85% of Social Security taxed under the IRS worksheet, the standard deduction with the extra amount at 65 and the senior deduction, the ordinary brackets, then qualified dividends and long-term gains at 0%, 15% or 20%, and the 3.8% net investment income tax. Below $100,000 of taxable income the tax comes from the IRS Tax Table, as the Form 1040 instructions require.

Medicare IRMAA brackets and the ACA 400% line are cliffs. One dollar over a line costs the whole step. The calculators compare your modified adjusted gross income with each line and show how far you are from it. State income tax uses each state’s own tables and its rules for Social Security, pensions and IRA withdrawals. Where a state has not yet published its tables for the year, the result says so and shows no state figure. California is the exception. It uses the latest published California tables and names their year.

Projections past this year, such as a multi-year Roth conversion path, hold the latest published tables constant and show amounts in today’s dollars.

How the engine is checked

The federal calculation has been compared with PolicyEngine-US, an open-source model of US tax law, on 20 sample households for tax year 2026. The pass line is federal tax within $1 per $1,000, the same adjusted gross income, taxable Social Security and taxable income, and the same IRMAA bracket. Where the two disagree, the case is settled against the IRS instructions or the statute.

Automated tests cover the engine’s tax rules, each state’s rules and the figures on this site, and they run before every release. Tables are updated within 30 days of the IRS publishing next year’s figures, usually in the fall. Each table records the day it was last checked against its source.

Sources and dates checked

Each calculator lists the tables it uses under “Tables and sources”. This is the full list.

State income tax, 2026

249 tables for the 50 states and DC, last checked on September 24, 2026. Each state’s tables and sources are listed on the retiree tax calculator when you choose that state.

What is not modeled

• Filing statuses other than single and married filing jointly.
• The federal alternative minimum tax, federal tax credits, and adjustments to income other than the HSA deduction.
• Most local income taxes, such as New York City’s.
• Forecasts of markets, inflation or future law. A multi-year projection grows balances at the real return you enter.
• Your actual accounts. You enter balances and income yourself; nothing connects to a bank or brokerage.

Each calculator’s method section names what else it leaves out. Rules can change after a table was last checked, so compare a figure with its source before you act on it.

Not tax advice

Dipperfield shows what your inputs produce under published rules. It does not recommend investments, advisers or a course of action.

Calculations, not tax, legal or investment advice.