IR35 Calculator Guide: How to Work Out Your Take Home Pay in 2025

An IR35 calculator helps UK contractors compare take home pay inside IR35 versus outside IR35. The difference can be substantial. A contractor billing £600 per day for 220 days a year (£132,000 turnover) might take home around £75,000 to £82,000 outside IR35 through a combination of salary and dividends, but only £65,000 to £72,000 if caught inside IR35 and paid through PAYE.

That gap of £10,000 or more per year is why IR35 status matters so much for limited company contractors. The rules determine whether you are treated as a genuine business or as a disguised employee for tax purposes. Get it wrong and HMRC can demand back taxes, interest and penalties.

This guide explains what an IR35 tax calculator measures, how inside and outside IR35 pay structures differ, and what inputs you need for an accurate result. Use our IR35 calculator to model your own day rate and working pattern.

What IR35 means for your take home pay

IR35, formally the off-payroll working rules, determines whether a contractor working through an intermediary (usually a limited company) should be taxed as an employee. If your contract is inside IR35, the fee-paying client or agency must deduct income tax and National Insurance from your payments before you receive them, as if you were on their payroll.

If your contract is outside IR35, you operate as a genuine business. Your limited company invoices the client, receives gross payment, and you extract profits through a tax-efficient combination of salary and dividends. You pay corporation tax on company profits and personal tax on dividends, but the overall tax burden is typically lower than PAYE.

For a detailed breakdown of the tax implications, see our guide on IR35 inside and outside tax implications. For broader contractor context, read our IR35 guide for UK contractors.

Outside IR35: how take home pay is calculated

Outside IR35, your limited company is the contracting entity. It invoices the client at your agreed day rate, minus VAT if registered. From the company income, you deduct allowable business expenses, pay employer National Insurance on your director salary, and pay corporation tax on remaining profits.

Most contractors pay themselves a small director salary up to the National Insurance secondary threshold (around £12,570 for 2025/26) and take the rest as dividends. Dividends are taxed at 8.75% in the basic rate band, 33.75% in the higher rate band, and 39.35% in the additional rate band, after a £500 dividend allowance.

Corporation tax is charged at 19% on profits up to £50,000 and 25% above £250,000, with marginal relief between those thresholds. For a typical contractor with £130,000 company income, £5,000 expenses, and a £12,570 salary, corporation tax applies to profits after salary and employer NI, and the remainder is available for dividends.

Inside IR35: deemed employment payment

Inside IR35, your take home pay is calculated differently. If the client is responsible for determining status (most private sector contracts since April 2021), they pay your limited company a deemed employment payment after deducting income tax and employee National Insurance. Your company receives net payment, not gross.

The deemed employment payment is treated as salary for tax purposes. Your company can deduct a 5% expenses allowance for notional administrative costs, but cannot deduct most other business expenses that would be allowable outside IR35. Employer National Insurance is also due on the deemed payment.

The practical effect is that inside IR35 pay resembles employment PAYE. You lose the dividend route entirely. All income flows through as employment income, taxed at source. For the same £600 per day contract, take home pay inside IR35 is typically £10,000 to £15,000 less per year than outside IR35.

Inside IR35 through an umbrella company

Some contractors caught inside IR35 work through an umbrella company rather than their own limited company. The umbrella becomes the employer, invoices the client, deducts PAYE and NI, and pays the contractor net. Umbrella company margins add £20 to £30 per week on top of tax, further reducing take home pay compared with outside IR35 through a limited company.

Umbrella working simplifies administration when every contract is inside IR35, but it is almost always the least tax-efficient option. If you have a mix of inside and outside IR35 contracts, a limited company with deemed payment processing is usually better than switching to an umbrella for all work.

Key inputs for an IR35 salary calculator

An accurate IR35 calculator needs your day rate or annual contract value, the number of days or weeks you work per year, and your estimated business expenses. It also needs to know whether you are calculating inside or outside IR35, or comparing both scenarios side by side.

For outside IR35 calculations, the calculator models director salary, employer NI, corporation tax, and dividend tax. You can usually adjust the salary level to see how different splits affect take home pay. For inside IR35, the calculator applies PAYE tax bands and employee NI to the deemed employment payment.

Pension contributions reduce taxable income in both scenarios. Salary sacrifice pension contributions through your limited company reduce corporation tax and personal tax. Inside IR35, pension contributions can be made from the deemed payment before tax, depending on how the client processes payment.

Worked example: comparing inside and outside

A contractor bills £500 per day for 230 days, giving £115,000 annual turnover. Allowable expenses outside IR35 total £6,000, covering accountancy fees, insurance, software, and travel. Director salary is set at £12,570.

Outside IR35: company profit before tax is roughly £96,430. Corporation tax at approximately 22% effective rate takes around £21,200. Dividends of roughly £75,230 are subject to dividend tax of about £7,500 after the £500 allowance. Take home including the salary is approximately £80,300.

Inside IR35: the deemed employment payment is approximately £109,000 after the 5% expenses deduction. PAYE income tax and employee NI reduce this to roughly £68,500 take home. The difference is approximately £11,800 per year, or nearly £1,000 per month.

Run your own figures through the IR35 calculator to see how your specific day rate, working days and expenses affect the gap between inside and outside IR35.

Who determines IR35 status

Since April 2021, private sector clients are responsible for determining IR35 status for medium and large businesses. They must provide a Status Determination Statement (SDS) explaining whether the contract is inside or outside IR35. Small business clients are exempt, and the contractor's company remains responsible for assessing status in those cases.

A small client is one that meets two or more of: turnover under £10.2 million, balance sheet total under £5.1 million, and fewer than 50 employees. If your client qualifies as small, you assess your own IR35 status and bear the tax risk if HMRC disagrees.

Public sector clients have been responsible for determining status since 2017. The rules are the same in principle: the client assesses, provides an SDS, and applies PAYE if inside IR35. Contractors can dispute a determination through the client's disagreement process, but cannot simply ignore an inside IR35 ruling.

The CEST tool and status assessments

HMRC provides the Check Employment Status for Tax (CEST) tool online. Clients often use it to support their SDS, though its accuracy is debated within the contracting industry. CEST asks questions about supervision, substitution, mutuality of obligation, and financial risk.

A contract outside IR35 typically allows genuine substitution, gives the contractor control over how work is done, lacks mutuality of obligation beyond the current engagement, and places financial risk on the contractor's business. No single factor is decisive. HMRC and tribunals look at the reality of the working arrangement, not just the contract wording.

Professional IR35 reviews from specialist accountants or lawyers provide more nuanced assessments than CEST alone. If you are negotiating a new contract, having it reviewed before signing can prevent an inside IR35 determination that costs thousands in lost take home pay.

Tax rates that affect IR35 calculations in 2025/26

Income tax bands for England, Wales and Northern Ireland in 2025/26 are: 0% on the first £12,570 (personal allowance), 20% basic rate to £50,270, 40% higher rate to £125,140, and 45% additional rate above. Scotland has different bands and rates.

Employee National Insurance is 8% on earnings between £12,570 and £50,270, and 2% above. Employer NI is 15% on earnings above £5,000 per year from April 2025. Inside IR35, both employee and employer NI are effectively borne by the contractor, reducing net pay further.

Corporation tax remains relevant only outside IR35. The 19% small profits rate applies to profits up to £50,000. The main 25% rate applies above £250,000. Most contractors with a single contract fall somewhere in between and pay an effective rate of 20% to 24%.

Expenses inside vs outside IR35

Outside IR35, a wide range of business expenses reduce your company's taxable profit. Accountancy fees, professional indemnity insurance, business software, equipment, training related to the contract, and travel to temporary workplaces are commonly claimed. The rules follow standard self-employment expense principles applied at company level.

Inside IR35, expense claims are severely restricted. The 5% flat rate deduction is the main allowance when the deemed payment model applies. You cannot deduct accountancy fees, insurance, or most other costs from the deemed employment payment. This is a significant part of why inside IR35 take home pay is lower.

If you are caught inside IR35 for part of the year and outside for other contracts, each engagement is assessed separately. Your limited company may process a mix of gross invoices and deemed payments within the same tax year.

Common mistakes when using an IR35 calculator

Using gross contract value without deducting working days is the most frequent error. A £600 day rate for 220 days is £132,000, not £156,000. Always multiply your day rate by realistic working days, excluding holidays, gaps between contracts, and sick days.

Ignoring employer National Insurance inside IR35 understates the cost. When a client processes a deemed payment, employer NI is deducted from the contract value before it reaches your company. Your calculator should account for both employee and employer NI in inside IR35 scenarios.

Assuming all contracts are the same status leads to incorrect planning. You might be outside IR35 with one client and inside with another. Calculate each contract separately and combine the results for your annual take home pay forecast.

How to use the IR35 calculator effectively

Enter your day rate and expected working days for the tax year. Add realistic expenses for the outside IR35 scenario. Set your preferred director salary, typically £12,570 to maximise the personal allowance without paying employee NI on the salary itself.

Compare the outside IR35 take home with the inside IR35 figure. The difference is your annual cost of being inside IR35. Divide by your working days to see the per-day impact. Use this figure in contract negotiations, financial planning, and decisions about whether to challenge a client's status determination.

The IR35 calculator updates with current tax rates and NI thresholds for 2025/26. Re-run your calculation when rates change in the Budget, when you move between contracts, or when your working pattern changes significantly.

Staying compliant and maximising take home pay

IR35 compliance starts with honest status assessment. If your working practices match employment, no contract wording will sustainably keep you outside IR35. Keep records of status assessments, contracts, and working practices if HMRC investigates.