Compare taxes and see how much you save moving from California to UK
California has the highest state income tax in the US (up to 13.3%), yet the UK's national income tax is far higher on its own — roughly $23,700 vs California's $5,762 at $100,000 income. The critical context: California residents pay state tax ON TOP of US federal tax (~$17,344 at $100K), bringing their total to about $23,106. So total California (state + federal) vs UK national tax is surprisingly close at $100,000. Americans moving from California to the UK still file US federal tax returns every year — this is a worldwide income obligation that does not disappear on relocation. However, the UK and US have a tax treaty, and Americans can claim foreign tax credits for UK taxes paid, typically eliminating double taxation. The net result for most California-to-UK movers: you swap state + federal for UK national + ongoing US filing obligations, with foreign tax credits doing the heavy lifting to prevent paying both in full.
Highest US State Tax
9 progressive brackets from 1% to 13.3%
Progressive Tax System
Basic rate 20%, higher rate 40%, additional rate 45%
At $100,000 income:
California state income tax ($5,762) is much lower than UK national income tax (~$23,700) at $100,000. However, US expats in the UK can offset UK taxes paid against US federal obligations via foreign tax credits — reducing double taxation. Total CA (state + federal) vs UK national is close: $23,106 vs $23,700.
| Income | CA Tax | GB Tax | Savings | 10-Year |
|---|---|---|---|---|
| $50,000 | $1,711 | $6,700 | -$4,989 UK costs more | -$49,890 |
| $75,000 | $3,349 | $14,000 | -$10,651 UK costs more | -$106,510 |
| $100,000 | $5,762 | $23,700 | -$17,938 UK costs more | -$179,380 |
| $150,000 | $10,991 | $44,000 | -$33,009 UK costs more | -$330,090 |
| $250,000 | $22,471 | $88,000 | -$65,529 UK costs more | -$655,290 |
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Transfer Money Internationally →Yes. All US citizens and green card holders must file a US federal tax return regardless of where they live in the world. Moving to the UK does not end your US tax filing obligation. However, the US-UK tax treaty and foreign tax credits allow most Americans to offset UK taxes paid against their US liability — preventing true double taxation. You will typically pay whichever is higher (US or UK rate), not both in full.
California is notorious for auditing people who claim to have left the state. To sever California tax residency, you must establish domicile elsewhere and have minimal ties to California. Simply moving to the UK is not enough — you must also change your driver's license, voter registration, professional licenses, and not spend significant time in California. The Franchise Tax Board may still claim you owe California tax on income earned in your year of departure.
California state income tax at $100,000 is approximately $5,762. UK national income tax at the equivalent income (around £78,000 at current exchange rates) is approximately $23,700 USD — nearly four times higher. However, California residents also pay US federal tax (~$17,344), bringing total CA burden to ~$23,106. The UK national rate and total CA+federal rate are remarkably close at $100,000.
Between £100,000 and £125,140, UK taxpayers lose their personal allowance (£12,570) at a rate of £1 for every £2 earned. This creates an effective 60% marginal tax rate in that band. Californians moving to the UK should be aware this trap applies to income between roughly $128,000 and $160,000 USD.
The Foreign Earned Income Exclusion (FEIE) allows qualifying US expats to exclude up to $126,500 (2024) of foreign earned income from US federal tax. However, if you claim the FEIE, you generally cannot also claim foreign tax credits on the excluded income. For UK-based Americans (where UK rates often exceed US rates), it is often more advantageous to use the Foreign Tax Credit rather than the FEIE.
Yes. UK National Insurance (NI) contributes to the state pension and NHS. Employees pay 8% on earnings between £12,570 and £50,270, and 2% above. US Social Security is 6.2% (capped at $168,600 in 2024) plus 1.45% Medicare. A US-UK totalization agreement means you generally don't pay into both systems simultaneously.
On pure income tax, high earners generally keep more in the US. At $250,000, California state tax is $22,471 (plus ~$65,000 federal = ~$87,471 total) versus UK national tax of approximately $88,000. The totals are similar at $250K, but at $500K+ the US pulls significantly ahead. The UK's 45% top rate kicks in above £125,140, while the US top rate of 37% kicks in above $578,125 for single filers.