I split the year between the UK and Bulgaria, under 183 days in each — where am I tax resident?

Your accountant laughed for good reason — being tax resident nowhere is a myth for people with homes, spouses and clients. The 183-day count is only one trigger among several. Bulgaria treats you as resident if you spend over 183 days here in any 12-month period, but also if your center of vital interests is in Bulgaria — family, home, where your economic and personal life is anchored. Your wife spending most of her time here pulls that factor toward Bulgaria. The UK meanwhile applies its Statutory Residence Test, where your available UK home, workdays and ties can make you UK resident well below 183 days. It is entirely possible to qualify as resident of both countries in the same year. When that happens, the UK-Bulgaria tax treaty tie-breaker decides in strict order: permanent home available (you have both, so it moves on), then center of vital interests, then habitual abode, then nationality. For you the decision will likely hinge on the vital interests picture — and with UK clients but a Bulgaria-based spouse, it is genuinely arguable either way, which means evidence wins. So document everything: a day-count diary with travel tickets and border stamps (note Bulgaria is in Schengen now, so passport stamps are gone for intra-Schengen hops — keep boarding passes), where you work from, utility usage in each home. Then take a position deliberately rather than by accident — 10 percent flat tax in Bulgaria versus UK bands makes the answer financially significant. Start with /guides/bulgaria-tax-guide-for-foreigners, then get a cross-border adviser to formalize it.