The system of record for a life built across borders.
Global wealth, tax exposure and estate planning, managed in one place. Know what a move costs before you make it — Mithduin computes the departure tax, the day counts and the filings that follow, from a record where every figure links to the document that proves it.
Six things every globally mobile entrepreneur must keep in order. Mithduin makes it easy.
Most people run their cross-border life across a lawyer's inbox, an accountant's spreadsheet, a broker's statement and a drawer of PDFs. Mithduin puts the whole picture under one roof, where each fact links to the document that proves it.
Residency & status
Day counts computed, never guessed.
Every jurisdiction you touch, from a travel log you keep once — including the US substantial-presence test, weighted and projected against travel already booked.
Tax filings, by year
What’s filed and what’s due — one look.
A ledger of every return, receipt and working paper, filed against the entity and the year it belongs to — with lead times on every deadline that matters.
Entities
The whole structure, legible at a glance.
Corporations, foundations and trusts drawn as the structure they actually form — charters, registers, agents and standing, with the ownership map kept current.
Portfolios
Synced read-only. Reconciled every morning.
Liquid holdings synced from Interactive Brokers on a read-only token — positions, cash and accruals across every account, consolidated into a single view.
Private assets
Every mark carries a policy and an appraisal.
The holdings statements never show — the operating stake, the apartment, the private credit note, the cold-storage wallet — each carried at a documented basis.
The document vault
The paper everything above rests on.
The vault versions and hashes each document at upload, links it to the record it proves, and makes it readable by Ask Mithduin.
A question, answered from your own record.
Ask Mithduin doesn't browse the web or guess. It reads your vault, your entity register and your live brokerage feed, computes the answer, and shows you the documents it used. Every response is a citation away from the source.
- → "What expires or comes due in the next 90 days?"
- → "How many US days are safe this year?"
- → "Show me every 2025 filing and its receipt."
- → "What's the Duin Foundation, and what does it hold?"
- → "What are the tax consequences for my companies, trusts and investments if I move to New York next year?"
- → "What would breaking Canadian residency on March 1 crystallise, at current marks?"
- → "Draft the questions I should take to my adviser about the new venture."
- → "Which documents in my vault expire in the next 90 days?"
US substantial presence for 2026. You've taken 38 days this year, plus 65 in 2025 (÷3) and 80 in 2024 (÷6).
That's a weighted total of 73 of 183 — the test is not met. 109 more US days keeps you under — the 110th meets the test.
Set up once with your advisors. Kept current from there.
Mithduin is built and run by its founder, working with trusted advisors with expertise in international tax law (IRS, CRA, HMRC and EU regimes), structuring, trust and estate planning, asset protection and finance. The software keeps the record exact; the people judge what it means.
We build your record
Our team sits down with your existing counsel and accountants, loads the structure, the filings and the documents, and reconciles the opening picture against reality.
It stays in sync
Portfolios pull from Interactive Brokers each morning. Travel updates day counts. New documents land in the vault. Deadlines surface themselves before they're due.
You — and they — just look
One place answers "where do I stand," for you and for anyone you bring in. No more assembling the picture from four inboxes every time a question comes up.
Held to the standard the contents demand.
This is the most sensitive record a person keeps. It is treated that way — encrypted, access-logged, and never used to train anything or sold to anyone.
Read the security noteEncrypted in transit & at rest
Documents and data are encrypted end to end; the vault records a SHA-256 for every file at upload.
Every access on the record
Sign-ins and every change are written to an activity log you can see. Two-factor and passkeys are next on the roadmap — we say so rather than claim them early.
Read-only by default
The brokerage connection is a read-only Flex token with no trading permissions — Mithduin can see, never move.
Your data stays yours
Nothing leaves the vault to train models or reach third parties. Ask Mithduin answers from your record and only your record.
“The grey river — a course that runs steady through changing country, carrying everything it holds without losing it.”
Your life and business span across borders. You need a platform and advice that does as well.
A private walkthrough of the record, arranged on request.