Method Deck / tax

Marginal vs. effective tax rate, by tax year

Computes both the marginal tax rate (the rate on the last dollar earned) and the effective tax rate (total tax divided by taxable income) using the published IRS brackets for a chosen tax year.

Try it

Inputs

• filing_status (string, required) one of: single, married_filing_jointly, head_of_household : Filing status
• taxable_income (number, currency units, required) min 0.01 : Taxable income for the chosen tax year (after deductions)
• tax_year (string, required) one of: 2026 : Which year's published IRS bracket table to use. Only 2026 is built into this method today; a later year requires adding its table.
• tax_year_source (string, required) : Citation for the tax_year bracket table (for example the IRS revenue procedure); change it together with tax_year when a newer year is added.
• tax_year_date (string, ISO date, required) : The date the cited tax_year table was retrieved or published.

Outputs

• tax_owed (currency units): Total federal income tax owed for the chosen tax year
• marginal_rate_percent (%): Tax rate applied to the last dollar of taxable income
• effective_rate_percent (%): tax_owed divided by taxable_income, as a percent

Steps

1. The visitor supplies tax_year (which published IRS bracket table to use) plus tax_year_source and tax_year_date, the citation for that table; this method never looks up or fetches a table itself.
2. Select the bracket table for tax_year and filing_status.
3. Find the bracket row where taxable_income falls; that row's rate is the marginal_rate_percent. Boundaries are inclusive of the upper bound: income exactly at a bracket's upper threshold is taxed and rated in that (lower) bracket, matching the IRS table's 'not over' wording; the next bracket applies only to income strictly greater than the threshold.
4. tax_owed = the row's base amount plus its marginal rate times (taxable_income minus the row's lower bound), rounded to 2 decimals.
5. effective_rate_percent = tax_owed / taxable_income * 100, rounded to 2 decimals.

Constants

• single_2026_brackets = 10% to $12,400; 12% to $50,400; 22% to $105,700; 24% to $201,775; 32% to $256,225; 35% to $640,600; 37% above rate schedule (source)
• married_filing_jointly_2026_brackets = 10% to $24,800; 12% to $100,800; 22% to $211,400; 24% to $403,550; 32% to $512,450; 35% to $768,700; 37% above rate schedule (source)
• head_of_household_2026_brackets = 10% to $17,700; 12% to $67,450; 22% to $105,700; 24% to $201,750; 32% to $256,200; 35% to $640,600; 37% above rate schedule (source)

Sources

• Rev. Proc. 2025-32, Section 4.01 (2026 Tax Rate Tables, Tables 1-3) (Internal Revenue Service, 2026-09-30T19:31:29Z) - Official 2026 tax year inflation-adjusted tax rate tables used for both the marginal rate lookup and the tax computation; documented source of the tax_year_source/tax_year_date default values prefilled below.

Worked example and test vectors

Published card

• Address: 57771bb59efa74ddef7bcdbcdbd2c6ec
• Made at: 2026-09-30T22:39:30.722Z
• Method sha256: e1448a0768d0c07a05d7f0f4e2de15ef72615b54816670eb8dc9c7b1902f7640