Your ISA holds stocks from multiple countries, but each one comes with a different invisible tax bill. A UK stock yielding 4% keeps every penny in your ISA — no withholding tax, no FX conversion. But a US stock yielding 4.5% only nets you 3.8% after 15% withholding tax and FX fees. The lower-yielding UK stock actually pays you more. And it gets worse: Switzerland withholds 35% upfront, turning a Nestle yield of 3.9% into just 2.5% — unless you manually reclaim the difference through a 6-to-12-month paperwork process. France is the European bright spot at 12.8%, while Germany sits at 15% after treaty reclaim. This episode introduces the breakeven yield rule: a US stock needs roughly 5.9% gross to match a UK stock at 5% net, and a Swiss stock needs 7.7% without reclaim. But going all-UK means heavy concentration in banks, energy, and mining — the FTSE 100's top 10 holdings make up nearly half the index. The real question isn't whether to avoid foreign stocks, but whether the diversification is worth the price tag. Use Nestor's portfolio view to see the net yield for every holding — after withholding tax and FX fees — broken down by country, so you can make that decision with real numbers.From the team behind Nestor – Dividend Trackerhttps://www.nestordividendtracker.co.uk