One life.
Two tax systems.
Keep more of what's yours.
Your 401(k), your ISA, your RSUs, your move date — small choices about each quietly change what each country gets to tax. Two Shores is a living library of the US, UK, and treaty rules that decide it, in plain English, with the source behind every answer. $99 a year for all of it, not a $2,000 advisor bill.
Education and decision-support, not regulated financial advice. Every answer shows its source.
Keep more of it
See where each country's rules actually reach your money, and where they don't.
File it right
The forms each side expects, in plain English, before a deadline turns into a penalty.
Time the big moves
A sale, a vest, or a move date can change the whole outcome. See how before you commit.
RULEBOOK: UNITED STATES
- JAN · RSU VESTUS-sourced, W-2
- APR · SELL INDEX FUNDSgains recognized pre-residency
- AUG · SEVER NY DOMICILEchecklist: 11 items
RULEBOOK: UNITED KINGDOM
- OCT · SPLIT-YEAR STARTSSRT case 4 · FIG clock: yr 1 of 4
- NOV · RSU VESTapportioned grant-to-vest
- JAN · ISA?⚠ PFIC — see finding
This is how Two Shores sees your life: one timeline, with each event read under the country whose rules apply. Change any event, like the move date, a share vest, or a sale, and everything after it updates under the right rulebook. You never re-enter future years by hand.
- Cited to IRC · HMRC · the US–UK treaty
- Checked by a cross-border tax professional
- Every answer versioned and dated
Does any of this apply to you?
If you have money on both sides, something here probably touches you.
You don't need to know the jargon. These are ordinary situations. Some are risks worth heading off early, some are life changes that quietly rewrite which rules apply, and others are retirement or savings moves people simply don't know are open to them.
You have a 401(k), IRA, or workplace pension.
How each is taxed turns on where you live and when you draw it. The timing is yours to plan.
You hold, or have avoided, an ISA or index fund.
What's tax-free on one shore can be taxed hard on the other. Knowing which changes what's worth holding where.
You get RSUs, options, or a bonus around a move.
The same grant can split between two countries by the dates. A few weeks either way changes the outcome.
You've already moved and kept filing the same way.
The UK's new FIG regime changed what's efficient for recent arrivals. Year-one right may not be right now.
You're thinking about moving back, or which year.
The tax year you land in, and what you sell before or after, moves the bill. It has a knowable answer.
You own a home in one country, rent in the other.
Each side treats the gain on a sale and the rent from letting differently. The overlap is where surprises live.
You're weighing a visa, a green card, or citizenship.
Each step changes which country's rules reach you, and some choices have long tails. Better to see the map first.
You're marrying, or married, across borders.
A couple split between two systems can be taxed very differently by who holds what, and where. The obvious choice rarely wins.
A new baby with a claim to two passports.
Dual citizenship from birth is a gift with paperwork attached — far easier to plan at the start than to untangle later.
None of this is advice, and not all of it is bad news. Two Shores shows which of these actually apply to your situation, each one with the rule and the source behind it, so you can see why.
Why this exists
The expensive mistakes happen before you knew there were rules.
Nothing warns you. Your US broker doesn't know you're leaving. Your new UK bank doesn't know what a W-9 means for you. And the forum thread you found is from 2019, before the rules changed.
You open an ISA and buy a UK index fund. Sensible in London. In Washington's eyes you now own a Passive Foreign Investment Company, one of the harshest corners of the US tax code, with the paperwork to match. Thousands of new arrivals do it every year.
You sell your appreciated portfolio two months after landing instead of two months before. Same shares, same gain, completely different tax outcome, decided by residency dates you didn't know were being counted.
You leave, but your state doesn't agree. New York and California keep taxing people who moved abroad without formally cutting ties with the state. The fix is a checklist, if anyone had shown it to you.
How Two Shores works
A rules engine underneath. Plain English on top.
Two Shores is not a chatbot with opinions. Every answer comes from a tested, up-to-date set of US, UK, and treaty rules, each one tied to the official source and checked by a cross-border tax professional. The AI does the explaining, never the deciding.
Know what applies to you
A living library of the rules that govern two-country money: PFICs, the Statutory Residence Test, the treaty's pension articles, the new FIG regime, matched to your citizenship, visa, and accounts. When a rule that affects you changes, you get an alert.
See your whole life at once
Describe your situation in plain words and Two Shores builds your timeline: accounts that know which country's rules they follow, income that knows its currency and source, and events that carry forward on their own.
Compare your options
Move in March or June? Sell before or after? Convert the Roth this year or next? Try each option side by side, compare the outcomes, and walk into any professional's office ten steps ahead.
Holdings in Vanguard FTSE All-World (ISA) become presumptive PFICs at your US residency start (Event: MOVE → US, 2027-06-14). Exposure basis: £84,200.
Options modeled: dispose pre-residency · elect mark-to-market · hold & file 8621.
↳ IRC §§1291–1298 · HMRC reporting-fund list (2026-04) · reviewed: E. Whitmore CTA, 2026-05-02
A real Two Shores answer. Not "it depends." Not a guess. A rule, a version number, your numbers, your options, and the sources to prove it.
The Library
One library. Every cross-border situation.
A move is where most people start, but it's one title on the shelf. The same engine reads a green card, a cross-border marriage, a child with two passports — each a playbook, each kept current as the rules move. One membership opens all of them.
The US→UK move
Residence, split-year, RSUs, the calendar.
Available now
The green-card decision
The long tail of a card, and the exit clock.
In preparation
A cross-border marriage
Two systems, one household, who holds what.
In preparation
A US-citizen baby
Dual citizenship from birth, and its paperwork.
In preparation
New playbooks land as the corridor demands them, and Library members get each one as it ships — plus an alert when a rule that affects their situation changes.
Plans
Priced like software. Because it is software.
You've seen the price of the advice it takes to answer all this. Here's the price of the answers.
Two Shores won't replace a great advisor for a genuinely complex estate. It answers the hundred questions that come before that one, for about the price of the parking.
Every playbook, every new release as it lands, and an alert the moment a rule that affects your situation changes. The whole rules library, kept current, for less than one hour with an advisor.
Explore the LibraryA single title for the move: what to weigh before you fly, what the timing turns on, and the calendar that makes it work. Fourteen sections and nine interactive tools, each showing the rule behind it, and yours to hand to your accountant.
Get the Move PlaybookPersonal tools are on the way: a living timeline built around your own accounts and dates, a way to compare two plans side by side, and reminders for the deadlines that are easy to miss, like a voluntary National Insurance top-up window or a filing cutoff. The Field Guide list below is where that news lands first.
Before you decide
The questions people ask first.
Is this financial or tax advice?
No. Two Shores is education and decision-support: it shows how the published rules apply to your situation, with the source behind each one, so your own decisions — and your conversations with professionals — start further ahead. For advice on your specific situation, we point you to someone regulated to give it.
Couldn't I just ask ChatGPT?
You can, and it will answer confidently either way. Two Shores' answers come from a versioned rules engine with citations to the IRC, HMRC manuals, and the treaty, checked by a cross-border professional — not a model improvising from a prompt.
My situation feels complicated.
Most cross-border situations are. When yours goes past what a playbook models — trusts, a business, a third country — Two Shores says so plainly and points you to a specialist, rather than guessing.
What do I get, and what does it cost?
The Library is $99 a year: every playbook, every new release, and an alert when a rule that affects you changes. Or buy a single playbook — the US→UK move is $49 one time, updated for twelve months. Each is interactive, shows the rule and source behind every answer, and exports to hand to your accountant.
What happens to my email address?
One note when we publish, one when a rule that affects your situation changes, and a one-click unsubscribe. No third-party trackers run on the pages you read.
The fine print, up front
Not advice. Clarity.
Two Shores doesn't tell you what to buy, and it isn't a substitute for a regulated adviser or a tax professional. It teaches and it helps you decide: how the rules apply to your situation, what your options are, and what the trade-offs look like, with a link to the actual IRC sections, HMRC manuals, and treaty articles behind every answer.
And when your situation goes past what we cover, like trusts, businesses, or a third country, Two Shores says so plainly and points you to a specialist rather than guessing. We think that honesty is the product.
The free US–UK Money Field Guide
Ten guides. Zero paywall. Start here.
PFICs and ISAs. What actually happens to your 401(k). The Statutory Residence Test, explained by someone who isn't billing you hourly. Get the Field Guide and a note when the rules move.
No account needed. One email when we publish, one when a rule changes. Unsubscribe forever in one click.