Rules last reviewed: 28 July 2026
How NetPay Lens calculates UK pay
NetPay Lens turns the details you enter into clear planning estimates. This page explains the rules, assumptions and limits behind the current calculators.
Current tax year and coverage
The current ruleset covers the 2026/27 UK tax year, from 6 April 2026 to 5 April 2027. The salary, pay-rise, job-offer and salary-sacrifice tools currently estimate PAYE for employees in England, Wales and Northern Ireland. The payslip tool estimates standard employee National Insurance category A for weekly, four-weekly and monthly payments.
Income Tax
We apply the standard Personal Allowance, the Income Tax bands for the selected tax year, and the reduction in Personal Allowance above £100,000. The tools support selected common tax-code treatments, including 1257L, BR, D0, D1 and 0T. Marriage Allowance can be included for an eligible receiving partner using the standard treatment.
National Insurance
Annual tools estimate employee Class 1 National Insurance. The payslip tool uses pay-period thresholds, which is important because National Insurance is normally calculated per pay period rather than cumulatively across the tax year.
Pensions
The tools can calculate employee contributions from full salary or qualifying earnings. The default automatic-enrolment illustration is 5% from the employee and 3% from the employer on qualifying earnings. Employer contributions are displayed separately because they do not reduce take-home pay. Salary sacrifice reduces the cash pay used in the estimate for Income Tax, National Insurance and loan deductions.
Student loans
Annual tools provide an annual estimate. The payslip calculator applies the relevant weekly, four-weekly or monthly threshold and rounds deductions down to whole pounds, as payroll does. A postgraduate loan can be modelled alongside an undergraduate plan.
What we do not currently model
Results can differ from a real payslip because we do not yet model every tax code, Scottish or Welsh tax calculations, multiple jobs, benefits in kind, bonuses, attachment orders, statutory payments, employer-specific pension rules, or every workplace deduction. Your employer's payroll and HMRC remain the authoritative sources for actual deductions.
Our sources
- HMRC: work out an employee's Income Tax
- HMRC: work out employee National Insurance
- HMRC: 2026/27 student and postgraduate loan tables
- GOV.UK: workplace pension contributions
Keeping the calculators current
We review rules when a new UK tax year begins and update this page when the ruleset changes. If you spot an error or have a question about an estimate, email admin@blitz.ws.