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Why inside IR35 costs you so much

This is not about disguising your status or gaming the rules. It is straightforward pension planning that happens to be unusually effective for inside-IR35 contractors, precisely because of how umbrella deductions work.

When you work through an umbrella company on an inside engagement, your day rate is not your salary. The agency assignment rate has to cover employer's National Insurance, the apprenticeship levy, and the umbrella's own margin before you reach your gross wage. Only then do income tax and employee National Insurance come off.

The gap this opens up against an outside-IR35 limited company is real, but it is far smaller than the contracting market generally claims. On 220 billable days with a £25 per week margin, it runs between £1,853 and £4,905 a year across the £400 to £800 per day range, at its widest at £650 a day and at its narrowest at £800. Our breakdown of inside versus outside take-home pay sets out the figures at four day rates with the assumptions behind each one.

That compression is what makes this strategy worth reading about. A gap of a few thousand pounds a year is a gap salary sacrifice can realistically close, which was never true of the five-figure gaps people used to quote.

How salary sacrifice changes the maths

With salary sacrifice, you agree to give up part of your gross wage in exchange for an equivalent employer pension contribution. Because the money is redirected before income tax and employee National Insurance are applied, you are not taxed on it now. The effect inside IR35 is stronger than most people expect for two reasons.

First, you save income tax at your marginal rate plus employee National Insurance on every pound sacrificed, rather than receiving it as taxed pay. Second, because the sacrificed amount also reduces the wage on which employer's National Insurance is calculated, many umbrella arrangements pass some or all of that employer's NI saving back into your pension too. That employer's NI saving has grown since the rate rose to 15% in April 2025, with the threshold at which it starts cut to £5,000, so the sums redirected by a sacrifice are larger than they were. That second effect is specific to the way inside-IR35 umbrella pay is structured, and it is why the same sacrifice can do more for an inside contractor than for a permanent employee.

The result is that a meaningful portion of the inside-IR35 penalty is not lost at all. It is diverted into your pension, where it would otherwise have been split between the Exchequer and National Insurance.

A worked illustration

Take a contractor on £500 a day across 220 billable days, paying a £25 per week umbrella margin. Inside IR35 through an umbrella with no pension arrangement, take-home is £65,620 a year. Outside IR35 through a limited company, after £1,500 of accountancy and £350 of insurance, it is £69,058. The gap is £3,438.

Sacrificing £11,000 a year into a pension costs £5,524 of that take-home. In other words you give up roughly £1 of spendable cash for every £1.99 that lands in your pension, because the sacrifice reduces income tax, employee National Insurance, employer's National Insurance and the apprenticeship levy at the same time.

Push that further and the gap disappears. At this rate a sacrifice of around £6,906 a year brings total compensation inside IR35, cash plus pension, level with the outside-IR35 cash figure. At £400 a day it takes about £8,229, at £650 a day about £7,308, and at £800 a day only about £3,425.

Two things to be straight about. Pension money is locked away until you can access it, so this is not a like-for-like swap for spendable income. And a limited company outside IR35 can make employer pension contributions too, marginally more efficiently, at about £2.12 of pension per £1 of take-home given up. Salary sacrifice is not an argument for preferring an inside role. It is the reason an inside determination now costs far less than most contractors assume.

Your own figures will differ with your day rate, working days, umbrella margin, and how your umbrella handles the employer's NI saving. The honest way to see your position is to model it.

That is exactly what the third scenario in our take-home calculator is built for. It compares three structures side by side: outside IR35 through your own limited company, inside IR35 through an umbrella, and inside IR35 with a salary sacrifice pension. You enter your day rate and the contribution you are considering, and it shows how much of the inside penalty the pension route recovers. No other IR35 tool models this scenario. For how the calculator applies this, we set out every rate and assumption behind the figures.

The April 2029 deadline on this strategy

This is a time-limited opportunity, and the clock is now visible.

From 6 April 2029, National Insurance relief on salary-sacrificed pension contributions is capped at £2,000 a year. Above that limit, the earnings you forgo become subject to Class 1 National Insurance, both primary (yours) and secondary (your employer's). Contributions above the limit remain permitted, and HMRC confirms the income tax relief is unchanged, so what they lose is only the National Insurance saving that makes the arrangement unusually effective for inside-IR35 umbrella workers.

That matters more here than it does for a typical employee, because the employer's NI saving is a large part of why the numbers above work. The income tax relief survives, so salary sacrifice will still be worth doing after April 2029. It will simply be a weaker lever than it is between now and then.

If you are inside IR35 and considering this, the tax years up to 2028/29 are the ones where the full effect is available.

Things to weigh before you commit

Salary sacrifice is powerful, but it is not free money and it is not right for everyone. The money is locked away until you can access your pension, so you need enough spendable income to live on now. Sacrificing below the level that would take your pay under the National Minimum Wage is not permitted, which can cap contributions at lower day rates. The pension annual allowance is £60,000, and our calculator caps its automatic sacrifice at that figure, which starts to bind from around £539 a day on 220 working days. Contributing above the allowance can still be legitimate if you have unused allowance to carry forward from the previous three tax years, but without it the excess draws an annual allowance charge. High earners also face a tapered allowance, which our calculator does not model. None of this is a reason to ignore the strategy. It is a reason to model it properly and, for anything significant, to confirm the detail with a contractor accountant or a regulated financial adviser. IR35 Verdict helps you understand your position. It does not provide financial or tax advice.

Run your own numbers across all three scenarios and you may find the inside determination you were dreading costs you a good deal less than the headline suggested.

Frequently asked questions

Can you use salary sacrifice when inside IR35? Yes. If you work through an umbrella company on an inside engagement, salary sacrifice into a pension is generally available and is one of the most effective ways to reduce the tax and National Insurance impact of inside status.

Why is salary sacrifice more effective inside IR35 than for a normal employee? Because inside-IR35 umbrella pay carries employer's National Insurance funded from the assignment rate. When you sacrifice salary you reduce the wage that employer's NI is calculated on, and many umbrellas pass that saving into your pension on top of the income tax and employee NI you already save.

Does salary sacrifice change my IR35 status? No. Salary sacrifice is a pay and pension arrangement. It does not affect whether your engagement is inside or outside IR35. It only changes how efficiently you are paid once your status is set.

How much will salary sacrifice actually save me? At £500 a day on 220 billable days, sacrificing £11,000 costs £5,524 of take-home, so you gain about £1.99 of pension for every £1 of cash given up. A sacrifice of around £6,906 a year brings total compensation inside IR35 level with the outside-IR35 cash figure at that rate. Your own numbers depend on your day rate, working days and umbrella margin.

Is salary sacrifice changing in 2029? Yes. From 6 April 2029, National Insurance relief on salary-sacrificed pension contributions is capped at £2,000 a year. Contributions above that are still allowed and still receive income tax relief, but they lose the National Insurance saving that makes the arrangement particularly effective for inside-IR35 umbrella workers.

Sources and further reading

• ·HMRC: Salary sacrifice reform for pension contributions, effective from 6 April 2029
• ·Deloitte: Charging NICs on salary sacrificed pension contributions
• ·HMRC: Salary sacrifice for employers
• ·HMRC: Rates and thresholds for employers 2026 to 2027
• ·IR35 Verdict calculator: model all three scenarios at your own day rate

IR35 Verdict provides estimates for illustrative purposes only. Nothing here is tax or financial advice. Speak to a qualified contractor accountant or regulated adviser before making pension decisions.