Apps / Tax return prototypeBeta

Your 2026 taxes, every number explained.

Name: Project 1040
Author: Tenziki Studio

A prototype that works out a 2026 U.S. federal return and returns for 41 states and DC in the browser, and shows the rule behind every number. It doesn’t file, and your answers never leave your device.

Open tax.tenziki.com ↗All apps

Project 1040 on the Review step: a federal refund of $909, with the Why? panel for the $9,000 no-tax-on-tips deduction open, showing the rule, the W-2 box 12 code TP tips and modified AGI it was built from, and its source, IRC §224

Screens

The Project 1040 home page: an ink hero reading Taxes, explained line by line, a tilted receipt showing a $909 federal refund with a lime Why? sticker, and lime, ink and cream tiles for Express, Guided and Expert — Home: Express, Guided and Expert, with a sample refund receipt

The Project 1040 home page on a phone, with the headline, Start with Express and Find every deduction buttons, and the $909 refund receipt — The same page on a phone

The Review step: the step list down the left with every step done, a $909 federal refund on an ink panel, and the return lines (wages $28,000, adjusted gross income $28,000, standard deduction $16,100, no tax on tips $9,000), each with a lime Why? button — Review: the refund up top, then every line with a Why? button

What it does

Project 1040

01
Every number has a why
Tap Why? beside any line to see what it was built from, the form and line it lands on, and the law it comes from.
02
Written for 2026
Brackets and the standard deduction from Rev. Proc. 2025-32, and the new One Big Beautiful Bill Act deductions for tips, overtime, seniors and car-loan interest.
03
41 states and DC
Resident, part-year and nonresident returns, with the credit for tax paid to another state. Move mid-year or work across a state line and each return is figured.
04
Express or Guided
Express covers W-2s, interest and unemployment in about 10 to 15 minutes. Guided asks what happened in your year: education, child care, Marketplace insurance, retirement, investments, crypto, self-employment and rentals.
05
Stays on your device
No account and no server. Answers are saved in your browser, and the PDF review copy of Form 1040 is built on your device.
06
Import or type a W-2
Import from payroll with the employer’s EIN and an import code, or type it box by box with checks against the W-2 rules. Try the sample employer: EIN 12-3456789, code DEMO-TIPS-2026, box 1 wages 28000.

Under the hood

Engine: TypeScript fact graph: every value records what it was built from, which powers the explanations
Federal: Form 1040 with Schedules 1, 1-A, 2, 3, 8812, A, B, C, D, E and SE, and Forms 2441, 5329, 8582, 8606, 8863, 8880, 8889, 8949, 8959, 8960, 8962 and 8995
Tests: 564 engine tests; golden returns checked against hand-worked figures
Front end: Next.js 16 and React 19, exported as a static site on Cloudflare Pages
Privacy: No accounts, no server storage, no third-party scripts; strict Content-Security-Policy
Status: Prototype. It doesn’t file with the IRS or any state, never asks for a Social Security number, and isn’t tax advice

Try it