"US shares" isn't one tax question, it's several, and moving to London doesn't collapse them into a single number. What you actually owe depends on which kind of US equity you're holding — RSUs still vesting, ESPP shares you already bought, or shares you're just sitting on — because UK tax treats each of those differently.
Unvested RSUs: still an employment income question
If you moved with RSU grants that haven't vested yet, nothing about the move changes the basic mechanic: vesting is the taxable event, taxed as employment income at that day's value. What the move can change is how much of a given tranche is UK-taxable at all — if you qualify as a qualifying new resident, Overseas Workday Relief sources each tranche over its own grant-to-vest window, and the portion of that window spent before you arrived can be exempt. See how RSU sourcing actually works for the mechanics — it isn't a flat fraction of your move-year income.
Shares you already own: a different part of the tax code entirely
ESPP shares already purchased, or any US shares bought outright before or after your move, aren't employment income going forward — they're capital. Two separate things can be taxable once you're UK resident:
- Dividends the shares pay out, taxed under UK dividend tax rules.
- Capital gains when you eventually sell, based on the gain since you acquired them (or, in some cases, since you became UK resident — the exact base cost treatment depends on your facts).
Neither of these is an Overseas Workday Relief question — OWR only applies to employment income sourced to overseas workdays, not to investment income or gains on shares you already hold.
The double-taxation question
US brokers commonly withhold tax on dividends, and sale proceeds can trigger US reporting obligations depending on your visa and residency status there. The US-UK tax treaty generally prevents the same income being fully taxed twice, but working out the actual credit is specific to the income type and your circumstances — this is squarely an accountant question, not something workday tracking touches.
Where FIG Tracker fits in
FIG Tracker handles the RSU and OWR side — tranche-by-tranche sourcing over the actual grant-to-vest window, so the portion of vesting income properly exempt on workday grounds is calculated correctly. It doesn't calculate dividend tax, capital gains, or US withholding credits; those sit with your accountant alongside your wider foreign income and gains treatment.
FIG Tracker is a calculation aid, not tax advice. Always verify your figures and the treatment of non-RSU holdings with a qualified tax advisor.