If you work as a UK contractor — or are considering it — the three letters that dominate every conversation are I, R, 3, and 5. Whether a contract falls inside or outside IR35 determines how you are taxed, what you can claim, and how much of your day rate actually reaches your pocket. The difference is not marginal: at a £500 day rate, the gap between inside and outside can exceed £12,000 per year in take-home pay. This guide explains what each status means, how the rules work in 2026, and what the real financial impact looks like. This is general information, not tax advice — speak to a qualified accountant.
What IR35 is — and why it matters
IR35 is the shorthand for the off-payroll working rules, named after the HMRC press release that introduced them in 2000. The core question is simple: if it were not for your limited company (or other intermediary), would you be considered an employee of the client? If the answer is yes, you are inside IR35 and should be taxed like an employee. If no, you are outside IR35 and can operate through your company with the tax efficiency that entails.
Since April 2021, the responsibility for determining IR35 status in the private sector shifted from the contractor to the end-client (for medium and large businesses). The client must produce a Status Determination Statement (SDS) and take "reasonable care" in reaching its conclusion. If HMRC later finds the determination was wrong, the client — not the contractor — is liable for the unpaid tax. This was a seismic shift, and it has made many large organisations risk-averse: when in doubt, they classify contractors as inside IR35.
Small companies (those meeting two of three criteria: turnover ≤£10.2 million, balance sheet ≤£5.1 million, or ≤50 employees) are exempt — the contractor retains responsibility for determining their own status.
Inside IR35: taxed like an employee
If a contract is inside IR35, the fee-payer (typically an umbrella company or agency) must deduct income tax and National Insurance contributions from your payments before they reach you — exactly as if you were on PAYE.
What this means in practice:
- Your day rate is treated as employment income.
- Income tax at 20%, 40%, or 45% is deducted, depending on your total earnings.
- Employee National Insurance (8% on earnings between £12,570 and £50,270; 2% above that) is deducted.
- Employer National Insurance (13.8% on earnings above £9,100) is also deducted — and this comes out of your rate before you see it.
- You cannot claim travel, subsistence, or accommodation expenses.
- You cannot pay yourself in dividends or claim the range of business expenses available to a limited company.
The result is that a significant portion of your day rate is lost to tax and NI before it reaches your bank account.
Outside IR35: limited company efficiency
If a contract is outside IR35, you invoice through your limited company, and the client pays your company gross. You then decide how to extract the money:
- A small salary (typically £12,570 to use your personal allowance) with minimal NI.
- The remainder as dividends, which carry no National Insurance and are taxed at lower rates: 8.75% basic rate, 33.75% higher rate, and 39.35% additional rate.
- Your company pays corporation tax (19–25% depending on profits) on its profits before dividends are distributed.
You can also claim legitimate business expenses through the company — travel, equipment, training, professional subscriptions, use of home as office, and pension contributions — all of which reduce your corporation tax bill.
The real numbers: £500/day inside vs outside
Here is what a £500 day rate looks like in 2026–27, assuming 220 chargeable days per year (£110,000 gross):
Inside IR35 (via umbrella):
- Gross contract value: £110,000
- Employer NI (13.8% above £9,100): ~£13,920
- Umbrella margin: ~£1,200
- Taxable salary: ~£94,880
- Income tax: ~£25,950
- Employee NI: ~£5,680
- Net take-home: ~£63,250
Outside IR35 (via Ltd Company):
- Gross contract value: £110,000
- Salary: £12,570 (PAYE-free)
- Company expenses: ~£5,000
- Taxable profit: ~£92,430
- Corporation tax (25% on profits above £50k, 19% below): ~£20,900
- Post-tax profit available for dividends: ~£71,530
- Dividend tax: ~£7,800
- Net take-home (salary + dividends): ~£76,300
The difference: roughly £13,000 per year — or over £1,000 per month — in favour of outside IR35. Over a three-year contract, that gap exceeds £39,000.
The risk landscape
The financial advantage of outside IR35 is clear, but it comes with responsibilities:
- HMRC investigation risk. If HMRC challenges a determination and finds a contract should have been inside IR35, the tax and NI owed can be substantial. Since April 2021, the liability generally falls on the client for medium/large businesses, but contractors using a limited company still bear responsibility for their own tax filings.
- No employment rights. Outside-IR35 contractors have no right to holiday pay, sick pay, maternity/paternity pay, or redundancy. You trade these protections for higher take-home pay.
- Administrative burden. Running a limited company requires annual accounts, corporation tax returns, confirmation statements, VAT returns, and payroll filings. Accountancy fees typically run £1,200–£2,000 per year.
Head-to-head comparison
| Factor | Inside IR35 | Outside IR35 |
|---|---|---|
| Tax treatment | PAYE — income tax + employee NI + employer NI deducted at source | Corporation tax on profits + dividend tax on extraction |
| Take-home at £500/day (220 days) | ~£63,250 | ~£76,300 |
| Expenses | Virtually none (no travel/subsistence) | Travel, equipment, training, pension, home office |
| Employment rights | Limited (umbrella worker rights) | None — self-employed |
| Admin burden | Low — umbrella handles everything | Moderate — Ltd Co accounts, filings, payroll |
| Investigation risk | Low (tax paid at source) | Moderate (status can be challenged) |
| Pension contributions | Via umbrella salary sacrifice | Company can contribute up to £60,000/year |
Who each suits
Inside IR35 suits:
- Contractors who want simplicity — the umbrella company handles all tax and admin.
- Those working for risk-averse clients (large banks, government departments) where outside-IR35 roles are rare.
- Short-term contracts where the admin overhead of a limited company is not justified.
- Anyone who values employment-like protections through an umbrella company.
Outside IR35 suits:
- Established contractors with multiple clients who can demonstrate genuine business autonomy.
- Those on long-term contracts where the annual tax saving justifies the administrative cost.
- Contractors who supply their own equipment, control their working hours and location, and can substitute another worker.
- Anyone maximising pension contributions — a limited company can contribute far more tax-efficiently than an umbrella salary sacrifice.
The verdict
The financial case for outside IR35 is compelling — a £13,000 annual difference at a £500 day rate is not marginal. But the determination is not yours to make: for medium and large clients, it is the client's call, and many have adopted blanket "inside IR35" policies to eliminate risk.
If you have a genuine outside-IR35 contract, the limited company route is almost certainly the right financial choice. If your client has determined you are inside IR35, you can challenge the SDS through the client's disagreement process, but in practice, many contractors accept the determination and work through an umbrella — the alternative is walking away from the contract.
The key is to understand the working practices that determine status — control, substitution, and mutuality of obligation — and to ensure your contract and your actual day-to-day working arrangements are consistent. A well-drafted contract reviewed by a specialist IR35 solicitor or accountant is worth every penny.