Two costs sit on top of every UK salary regardless of company size: uncapped Employer National Insurance above a low £5,000 threshold, and a minimum 3% pension contribution, though only on the band of earnings between £6,240 and £50,270, not the full salary.
The Apprenticeship Levy works completely differently, it's assessed on a company's total UK pay bill, not per employee, and only kicks in once that pay bill exceeds £3,000,000/year, with a further £15,000 annual allowance on top. A small team is almost certainly under that threshold; a larger employer with substantial UK headcount is very likely over it, and the levy becomes a genuine ongoing cost line on every subsequent hire, the same pattern as Australia's state payroll tax or Canada's Employer Health Tax.
What this calculator deliberately leaves out is Employment Allowance, a genuinely valuable offset worth up to £10,500/year against an eligible small employer's total NI bill. It's excluded for the same reason the Apprenticeship Levy is toggled rather than defaulted, it's a company-wide figure, not something that cleanly attaches to one specific hire's cost.