Every payroll calculator gives you a final number and asks you to trust it. PayPencil shows the working exactly like doing it by hand. Enter gross pay and tax code, see the personal allowance split, each tax band's slab amount and rate, then the total. For SMP, give the due date and earnings. PayPencil finds your Qualifying Week, Relevant Period, Average Weekly Earnings, and generates the full 39-week schedule with every payment shown. Built by a UK payroll pro, for UK payroll pros.