I moved to the UK for work last year and eventually learned about the FIG regime, and something called Overseas Workday Relief: basically a way to exclude the part of your income earned from days worked outside the UK from UK tax, for your first four years of residence. Sounded straightforward until I actually tried to calculate it.
I got quotes from a few accountants, one thousand pounds, another close to three thousand, just to work out the overseas fraction. Not even filing the return, just the calculation. That felt absurd for what is fundamentally a workday count and a currency conversion.
So I tried doing it myself and quickly understood why they charge that much. Each RSU tranche has to be sourced over its own grant-to-vest window, some of which started years before I even moved here. Bonuses are sourced to a completely different period, whenever the performance year was, not when they were paid. And every figure has to reconcile against the actual rate my employer used on the payslip, not some single official rate, since HMRC allows a few different bases depending on what you're converting. I had weekends, bank holidays, and sick days to exclude too, for every single period, separately. It stopped being a fraction and became a small research project.
I built FIG Tracker, a free OWR calculator, to handle the parts that are just mechanical: a workday calendar where you only log the exceptions, RSU and bonus sourcing done properly across tax years, and a day-by-day evidence report you can actually hand to an accountant. It's free, no catch — I built it because I needed it. If you want the detail on why RSU and bonus sourcing is the hard part, here's how the calculation actually works.
FIG Tracker is a calculation aid, not tax advice. Always verify your figures with a qualified tax advisor before filing with HMRC.