The method
We run the same steps for 2026 and for 2027, each with its own year's numbers.
- Standard deduction for your filing status, plus the extra amount for each box that applies: you 65 or older, you blind, and (on a joint return) your spouse 65 or older or blind. The extra amount is the higher “unmarried” figure for single and head of household, the “married” figure otherwise.
- Senior deduction: $6,000 for each person 65 or older, minus 6% of income over $75,000 ($150,000 joint), never below zero. Not available when married filing separately. Applies 2025 to 2028. This follows Schedule 1-A, lines 31 to 37.
- Charity without itemizing: your cash gifts, up to $1,000 ($2,000 joint), from 2026.
- Taxable income = income minus all of the above, never below zero.
- Tax from that year's brackets: the IRS Tax Table under $100,000 of taxable income, the Tax Computation Worksheet (the rate schedule) from $100,000 up.
- Child Tax Credit for children under 17: the per-child amount, reduced by $50 for every $1,000 (or part of $1,000) of income over $400,000 joint or $200,000 otherwise. It first cancels tax; what's left can come back as a refund, up to the refundable cap per child and 15% of earned income over $2,500 (Schedule 8812).
- The comparison: (2027 tax minus any refundable credit) minus (2026 tax minus any refundable credit). Per paycheck is that difference divided by your number of paychecks, to the cent.
Rounding
- Amounts you type are rounded to whole dollars (50 cents rounds up).
- Tax Table (taxable income under $100,000): the IRS taxes the midpoint of a row and rounds to the dollar. Rows are $0 to $5 (tax $0), $5 to $15, $15 to $25, then $25 wide up to $3,000, then $50 wide up to $100,000. We reproduce the 2025 IRS Tax Table exactly, including the IRS example: married filing jointly, $25,300 of taxable income, $2,562.
- From $100,000 up, the exact rate-schedule tax is rounded to the dollar.
- The senior deduction phase-out (6%) is rounded to the dollar.
- Under $100,000 the IRS Tax Table rounds to $50 rows, so “tax from brackets” can differ from the bracket chart's sum by a few dollars.
- Effective rate is rounded to one decimal place; per-paycheck amounts to the cent.
Simplifications
- Age: we use birth year only. Officially you are 65 on the day before the 65th birthday (i1040gi, Schedule 1-A instructions), so someone born on January 1 counts as 65 a year earlier; the calculator tells you to pick the year before.
- Married filing separately: your spouse's age or blindness isn't counted (a rare exception applies when the spouse has no income and isn't a dependent).
- Qualifying surviving spouse: we use the $1,000 charity cap, because the law gives $2,000 to a “joint return.” Some sites use $2,000.
- Child Tax Credit: same number of children both years; the Social Security tax method for three or more children (Schedule 8812 Part II-B) isn't modeled.
- Income: we treat your income as both adjusted gross income and modified AGI, and (if you tick “mostly wages”) as earned income.
About the 2027 projections
Projected The IRS usually publishes next year's numbers in October or early November. The IRS hasn't announced a date for 2027.
The law sets next year's brackets from the average chained consumer price index (C-CPI-U) for September through August. The Bureau of Labor Statistics never published October 2025 prices (the government shutdown), so Bloomberg Tax and Thomson Reuters averaged the 11 months that exist. How the IRS handles the missing month isn't known yet, so official numbers may differ by one rounding step ($25 to $50).
The closest call is the head of household standard deduction: our check gives about $24,945, which rounds down to $24,900, just $5 from the $24,950 step that Bloomberg Tax and Wolters Kluwer mention. The 2027 Child Tax Credit amounts come from one source (Thomson Reuters).
| Publisher | Date | Status |
|---|---|---|
| Bloomberg Tax (opens in a new tab) | 2026-09-11 (corrected 2026-09-22) | Verified (secondary) |
| Thomson Reuters Checkpoint (opens in a new tab) | 2026-09-11 | Verified (secondary) |
| Wolters Kluwer (opens in a new tab) | 2026-09 | Unverified |
When the IRS published past years' numbers:
- Tax year 2026: IR-2025-103,
- Tax year 2025: IR-2024-273,
- Tax year 2024: IR-2023-208,
- Tax year 2023: IR-2022-182,