Clear assumptions.
Better comparisons.

What is IR35?

Off-payroll working rules address engagements where a worker supplies services through an intermediary and would be an employee if engaged directly. Status depends on the actual engagement and working practices. HMRC off-payroll guidance.

Inside vs outside IR35 and umbrella pay

Inside IR35 usually means employment taxes apply. An umbrella assignment rate funds employer costs before worker gross pay; a gross PAYE rate excludes those employer costs. This calculator assumes all annual holiday pay is eventually paid. Accrued holiday pay changes payment timing, not annual economic earnings.

Day rate vs salary and working days

Only billable days produce contract revenue. Remove leave, bank holidays, sickness, administration and gaps from the year's weekdays. A short contract does not guarantee a full year's work. The calculator's days represent your expected total across the tax year, rather than a promise of continuous employment.

Pensions and benefits

Permanent employee pension uses a net-pay arrangement, with contributions based on base salary. Salary sacrifice is additional and reduces tax and NI pay. Company pension contributions are assumed to qualify for tax relief. Annual allowance charges, taper, carry-forward, MPAA and relief-at-source arrangements are outside this model. Benefits are gross non-cash values, not cash take-home.

Limited company expenses and Corporation Tax

Enter allowable business expenses only. The model assumes a 12-month accounting period, no opening reserves, no losses, no exempt distributions and one director. Corporation Tax includes marginal relief and adjusts thresholds for other associated companies. VAT and capital allowances need separate consideration. Retained profit may incur further tax when later withdrawn.

Personal tax assumptions

Standard personal allowance, annual category A NI and ordinary non-savings income are used. Savings interest, special tax codes, marriage allowance, Scottish cross-border residency rules and NI categories other than standard category A or State Pension age are not modelled. Other income determines tax bands but is excluded from scenario cash. Figures are incremental tax against the same other-income baseline. Real payroll deductions depend on pay periods and rounding.

Tax sources and verified year

Tax year 2026/27 · Last verified 5 October 2026 · Methodology · Official sources

View official sources and effective dates.

Privacy

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Interactive Blazor calculations run on the server, so financial inputs travel over the connection and remain in the temporary session. They are not deliberately persisted or logged. Normal hosting access logs can include IP addresses and requested URLs. Avoid putting confidential values in shared links. Local saves stay in your browser and can be deleted there. Analytics preferences are also stored locally. Google's privacy policy.