United States federal tax, tax year 2026, and nothing else. It does not compute state or city income tax, it is not for 2025 or 2027, and it is not for any other country. That is on the workbook title, the first line of the Start here sheet, a red banner at the top of every sheet and against every one of the thirty constants on the Sources sheet. The State dropdown even includes "Other / outside the United States", and choosing it puts a line on the sheet telling you plainly that this file is not for you.

Because that cell is the reason every other template on the market is worth $12. "Set aside 30%" is a guess dressed up as a spreadsheet: it does not know that your Social Security tax stops at $184,500 of net earnings, that the 0.9% Additional Medicare Tax starts at $200,000, that the section 199A deduction takes a fifth off your taxable income and then phases out, or that your bracket is not your marginal rate. This workbook computes all of it from the published forms. The rate it gives you is an output, not an input.

Four equal quarterly payments assume you earn evenly through the year. If you earned almost nothing until July and then landed a large project, the flat method makes you pay the IRS in April out of income you had not yet received — and if you do not, you are charged an underpayment penalty for a quarter in which you genuinely had nothing. Form 2210 Schedule AI lets you charge each instalment against what you had actually earned by that date. On the sample data in the file, the flat method wants $10,013 on 15 April and Schedule AI wants $509. It is an IRS form, not a loophole: you attach Form 2210 to your return with box C ticked in Part II. This workbook computes every line of it, which as far as we know no other spreadsheet does.

Three ways. First, every constant is on the Sources sheet with the IRS or SSA document it was read from, the URL and the day it was verified — check any of them yourself. Second, the workbook was built against an independent Python model of the 2026 tax written from the primary sources, and the build refuses to produce a file unless 20 scenarios agree cell by cell, to the dollar: 3,440 assertions in all. Third, the Checks sheet in your copy runs 29 reconciliations live, the strongest of which test Schedule AI column (d) against the full-year return line by line. If you change an input and something stops agreeing, you will see it.

Ten things, listed in full on the Start here sheet. The big ones: it computes tax BEFORE credits, so if you have children or qualify for the premium tax credit your real bill is lower. No state or city tax. Ordinary rates only — no preferential rate on capital gains or qualified dividends. No Net Investment Income Tax and no AMT. Itemised deductions are taken as one number without applying the SALT cap, the new 0.5%-of-AGI charitable floor or the section 68 reduction. One trade or business, no aggregation, no loss carryforward, no K-1s. And it works out what to pay so there is no penalty; it does not compute the penalty itself.

No, and it says so on four separate sheets. It reproduces the arithmetic printed on published IRS forms. It does not decide whether your business is a specified service trade or business, whether you materially participate, or whether a particular expense is ordinary and necessary. What it will do is make the conversation with a preparer much shorter, because you will arrive with the working already done — and the print pack has a page listing the four questions actually worth their fee.

Section 199A(i), the new $400 minimum QBI deduction, was added by the OBBBA in July 2025 and applies for the first time in 2026. There are no regulations on it, no IRS guidance and no case law, and the 2026 Form 8995-A had not been published when this engine was built. For one specific taxpayer — a specified service business with taxable income above the top of the phase-out range — the statute can be read two ways. This engine gives no deduction; PolicyEngine US gives $400, worth about $140 of tax. We take the reading that makes you pay more, we write it up on the Sources sheet with the statutory argument on both sides, and we tell you to ask your preparer. Six such places are documented; that is the one with money on it.

Yes. Upload the .xlsx to Google Drive, open it and choose File → Save as Google Sheets. Every formula is a classic one — ROUND, IF, INDEX, MATCH, COUNTIF, MIN, MAX, SUM, AND, OR, NOT, TEXT, ABS, ISNUMBER, IFERROR, ROW — with no macros, no XLOOKUP, no FILTER, no dynamic arrays and no external links, so the tax comes out to the same dollar in Excel 2016, Excel 365, Excel for Mac and Sheets. The file is recalculated in LibreOffice as part of every build and must report zero formula errors, both as shipped and with every input cleared. A set-up PDF walks you through it, sheet by sheet.

No, and this catches almost everyone. Form 1040-ES divides the year into 1 January–31 March, 1 April–31 May, 1 June–31 August and 1 September–31 December. The second period is two months, the fourth is four, and the payment for the last one is not due until 15 January of the following year. The whole workbook is built on those four periods, which is what makes the annualised method work properly.

2026 is a two-rate year: 72.5 cents per business mile driven before 1 July (IRS Notice 2026-10) and 76 cents from 1 July onward (IRS Announcement 2026-11 raised the rate mid-year). The Schedule C Summary sheet carries both in two ordinary input cells, pre-filled with those verified figures and dated on the Sources sheet, with the miles split to match — and a live check on the Checks sheet refuses miles in a half-year whose rate cell is empty. The cells stay inputs on purpose: when the IRS sets the 2027 rate next December, you overtype two cells and nothing else moves.

Yes. It is a fictional single freelance consultant in Colorado: $200,500 of gross receipts, $28,500 of expenses across the real Schedule C categories, $172,000 of net profit — and a deliberately brutal shape, with $150,000 of it arriving between June and August, so the annualised method visibly does something the moment you open the file. Every sample value sits in a yellow input cell. Clear Start here C16:C25, the yellow blocks on Income & Expenses by Period and Schedule C Summary, and the Payment Calendar, and the file is yours. The Start here sheet lists the exact ranges.

Yes, and it is handled properly, which is unusual. Your own W-2 Social Security wages eat into your $184,500 wage base on Schedule SE line 8d; your spouse's do not, because Schedule SE is a per-person form and a joint return carries one for each of you. Both sets of wages count towards the Additional Medicare Tax threshold, because that one is a household test. Federal income tax withheld from either job comes off the safe harbour pound for pound — and raising withholding is usually easier than making quarterly payments, because withheld tax is treated as paid evenly across the year.