What IR35 changes
IR35 rules consider whether a contractor would be an employee if the intermediary company were removed. An inside IR35 engagement is generally taxed more like employment, while an outside IR35 company can use normal company profit and distribution rules.
Inside and outside IR35 costs
Inside IR35 calculations can involve employer costs, umbrella margins, Income Tax and employee National Insurance. Outside IR35 calculations can involve company expenses, salary, Corporation Tax and dividend tax.
Status depends on working practices
A calculator cannot determine status. Control, substitution, mutuality of obligation, financial risk and the actual working relationship all matter alongside the written contract.