IR35 is the UK tax legislation that determines whether contractors are taxed as employees or as genuine businesses. Getting it wrong is expensive — in either direction. This IR35 calculator covers both the 2025/26 and 2026/27 tax years, including the April 2026 small company threshold changes.
Outside IR35: The Tax-Efficient Route
Operating outside IR35 through a limited company lets you take a tax-efficient mix of salary and dividends, claim allowable business expenses, and pay corporation tax on profits rather than income tax on all earnings. Most outside IR35 contractors retain 70–80% of their gross day rate. Use the Outside IR35 (Ltd Co) tab above to calculate your exact take-home for 2025/26 or 2026/27.
Inside IR35: Employee Tax Without the Benefits
Inside IR35, your income is treated as employment income — you pay full PAYE income tax and employee NI. On top of that, employer NI at 15% is deducted before you see a penny, typically costing you an extra £6,000–£12,000/year compared to outside IR35. The Inside vs Outside IR35 tab shows you the exact gap at your day rate.
The April 2025 NI Changes
Employer National Insurance rose from 13.8% to 15% in April 2025, with the secondary threshold dropping from £9,100 to £5,000. This increased the cost of being inside IR35 or working through an umbrella company by £1,500–£3,500/year at typical contractor day rates. Both our inside IR35 calculator and umbrella calculator reflect these 2025/26 rates.
The Three Key IR35 Tests
Control: Does the client dictate how, when, and where you work? More control = more likely inside IR35.
Substitution: Can you send a suitably skilled substitute to do the work? A genuine substitution clause helps outside IR35.
Mutuality of Obligation: Must the client offer work, and must you accept it? Yes = inside IR35. Note: HMRC's CEST tool notoriously ignores this test.
Umbrella vs Limited Company
If your contract is inside IR35, an umbrella company handles PAYE and NI administration. The main cost is the umbrella margin (£15–30/week). From April 2026, agencies must apply PAYE directly to all umbrella workers — use the Umbrella Company tab to calculate your net pay. Outside IR35, a limited company is nearly always more tax-efficient. See what's changing in April 2026 →
Day Rate to Salary Calculator
Not sure if a contract is worth taking over a permanent role? Use the Day Rate / Hourly / Annual tab to convert your day rate to an annual equivalent — accounting for the days you actually work, not just 260. As a rough rule, a £500/day contract (220 days) is equivalent to roughly a £71,500 permanent salary once you factor in holidays, pension, and job security.