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If you are working inside IR35 through an umbrella company and you have looked closely at your payslip, you have probably had the same reaction thousands of contractors have: your day rate is £500, so where has all of this gone, and why am I seeing "employer's National Insurance" listed as a deduction when I am not the employer? The frustration is completely understandable. It can genuinely feel like you are being charged for a tax that is supposed to be someone else's.

Here is the honest answer to the question everyone actually wants answered. Is it legal? Mostly yes, but the precise mechanism matters, and so does one distinction that almost nobody explains properly. Let us walk through it.

Why it feels like theft

The emotional core of this is simple. You negotiated a rate. You think of that rate as your money. Then a chunk of it disappears under a heading that says "employer", and your instinct says: I am not the employer, so this is not my cost.

That instinct is reasonable, and any explanation that just tells you to stop complaining is not being straight with you. But it rests on a misunderstanding about what the rate you were quoted actually is. Once that clears up, the whole picture changes, and so does where your real options lie.

The distinction that explains everything: assignment rate versus gross pay

When you work through an umbrella, there are two different numbers, and they are not the same thing.

The assignment rate (sometimes called the umbrella rate or the contract rate) is the amount the agency pays the umbrella company for your services. It is not your salary. It is the umbrella's income for placing you.

Out of that assignment rate, the umbrella, which is your actual employer, has to meet the costs that come with employing you:

• —Its own margin (the fee it keeps for running the payroll and employment).
• —Employer National Insurance, charged at 15% for 2026/27 on earnings above the £5,000 secondary threshold.
• —The apprenticeship levy of 0.5%.
• —Any employer pension contribution, if you have one.

Only after those employment costs are accounted for does the umbrella arrive at your gross taxable pay. From that gross figure, the normal deductions then apply: PAYE income tax and employee National Insurance.

So the sequence is: assignment rate, minus margin and employment costs, equals your gross wage, minus tax and employee NI, equals your take-home.

Employer NI is not coming out of your gross wage. It is being accounted for from the assignment rate to arrive at your gross wage in the first place.

So is it actually legal?

This is where precision matters, because the law draws a line exactly here.

An umbrella company cannot lawfully deduct employer NI from your contracted gross wage. If your contract sets a gross wage and the umbrella then strips employer NI out of that figure, that is a problem.

What an umbrella can and must do is account for employer NI out of the assignment rate before your gross wage is set. Employer NI is a genuine, statutory cost of employing you. The umbrella has no income other than the assignment rate, so that rate is the only place the cost can be funded from. Paid out of the assignment rate before your gross is calculated, it is the standard, compliant mechanism that every compliant umbrella uses.

The whole question therefore turns on what your paperwork describes the rate as. If you were quoted and contracted on an assignment rate, the employer NI being funded from it is lawful and normal. The number you mentally banked as "yours" was never your gross wage. It was the umbrella's income, out of which your employment was always going to be paid.

This is also why the Key Information Document matters. Before you sign, an agency must give you a Key Information Document that breaks down how the assignment rate translates into your gross and then your net pay. If you read it before accepting, the deductions should hold no surprises. If you are seeing them for the first time on a payslip, the failure was in the explanation up front, not in the deduction itself.

The honest part: this is not a grievance you can recover

It is important to be straight with you here, because plenty of forum threads are not. The employer NI funded from your assignment rate is not money you can claim back from the umbrella. There is no remedy against a compliant umbrella for operating the mechanism correctly, because it is doing what the law requires. Treating it as a wrong to be reversed will only cost you time.

The useful response is not to fight the deduction. It is to pull the levers that actually move your take-home.

What actually changes your position

Three things genuinely matter, and none of them is a complaint to your umbrella.

First, check whether you should be inside IR35 at all. The entire umbrella deduction stack only applies because the engagement is being treated as inside IR35. If that determination is wrong, everything downstream is wrong too. It is worth confirming your likely status rather than accepting it. You can run your contract through the checker to see a probability-based read of where you stand, with the relevant case law cited.

Second, understand the real gap between structures. The difference between an outside-IR35 limited company arrangement and an inside-IR35 umbrella one is large, and seeing it in pounds rather than in the abstract is sobering and useful. Our breakdown of inside versus outside IR35 take-home shows the figures at real day rates.

Third, and most powerfully if you are stuck inside, use salary sacrifice. A salary sacrifice pension can claw back a substantial portion of the inside-IR35 hit, because contributions are made before tax and National Insurance, including the employer NI element. For many contractors this recovers far more of the gap than they expect. Our guide to a salary sacrifice pension inside IR35 explains the mechanism and lets you model your own numbers.

The bottom line

Employer NI coming out of your day rate through an umbrella is lawful when it is funded from the assignment rate rather than stripped from a contracted gross wage. The feeling that it is unfair comes from a quoted rate that was never your salary in the first place. The deduction is not a battle to win. The genuine question is whether you should be inside IR35 at all, and if you are, how much of the hit you can recover. To see all of that in real numbers for your own rate, model your day rate across all three scenarios and compare the outcomes side by side.