One life.
Two tax systems.
Zero guesswork.
Longhand decides FEIE vs FTC, flags all 14 US and UK filings, and shows the law behind every number.
Trusted calculations. Transparent reasoning.
Deterministic engine
Every figure on your tax return is calculated by a rigorously audited deterministic engine. No language model ever touches a number.
Backed by official tax guidance
Each calculation is linked to the relevant IRS, HMRC, or tax treaty guidance, so you can see exactly why a deduction, credit, or liability applies.
Tax explanations in plain English
Complex tax rules become easy to understand. Highlights the reasoning behind each figure, and helps you confidently discuss your return with your accountant or tax adviser.
Every number defends itself.
Expand any form line and read the exact paragraph of law that produced it, from the wages on Form 1040 line 1h to the credit on Form 1116 line 35.
Your ISA is not invisible to the IRS.
UK platforms call it tax-free. US law calls the funds inside it PFICs and expects Form 8621. Longhand checks the $25,000 threshold and tells you before a penalty letter does.
Filing in both countries is a $1,500 problem.
- Consumer tax software refuses complex expat cases outright.$115+/yr
- A specialist accountant works, but the answer is a black box.$500 to $1,500/yr
- A generic chatbot is free, confident, and wrong where it counts.$0
Priced against the black box.
Illustrative pricing for the hackathon build. The engine is open source.
Free
$0
The decision, in two minutes.
- FEIE vs FTC verdict with reasoning
- All 14 US and UK filing flags
- No signup, nothing stored
Filer
$149/yr
Both returns, defended line by line.
- Everything in Free
- Full calculation trace
- Line-by-line previews of 13 forms
- Filled PDFs and a filing packet
- Plain-English explanation of every figure
Investor
$349/yr
On the roadmap.
- Everything in Filer
- PFIC excess-distribution computation
- Brokerage import
- Credit carryforward tracking
Questions
Is this tax advice?
No. Longhand produces deterministic estimates with citations so you can verify every step, then review with a professional. It does not file on your behalf.
Which forms does it cover?
14 filings across the IRS, FinCEN, and HMRC: Form 1040 and Schedules 1, 1-A, 2 and 3, Forms 2555, 1116, 8621, 8833 and 8938, the FBAR, and UK SA100, SA106 and SA109.
Does the AI compute my taxes?
Never. Pure Python computes every figure in exact decimal arithmetic. The language model receives finished numbers and citations, and returns only prose.
What is a PFIC?
A passive foreign investment company. Most UK funds and ETFs, including those inside a Stocks and Shares ISA, qualify, and the IRS taxes them punitively unless reported on Form 8621.
Where does my data go?
In the demo build, nowhere. Inputs are processed in memory against the analysis API and never stored.