Yep, been dealing with UK leave and PTO for about 3 years now. You're right about the 28 days—this includes the usual 8 bank holidays unless you specify otherwise in the contract. The tricky part is carry-over. By law, up to 4 weeks can be carried over for 18 months, but only under certain conditions (like if someone was too ill to take it). I found this resource really helpful when setting things up: https://theemployerofrecord.com/payroll-services-in-the-uk
United States