An umbrella calculation has one honest starting point and every misleading illustration begins by skipping it: the assignment rate is the amount the umbrella receives, not your pay, so the calculation runs downwards through the employment costs it funds before anything can be called gross.
Start at the assignment rate, as any umbrella pay calculator does
Enter the rate the agency quoted and the days or hours you will work in the period. If you were quoted a rate and separately told a take-home figure, the gap between them is what this calculation is for, and any illustration that starts at your gross pay has already hidden the part you wanted to see.
Take out the employer costs
Employer National Insurance, the Apprenticeship Levy where it applies, employer pension contributions where you are enrolled, and the funding of your statutory holiday. These are the umbrella's costs as your employer and they come out of the assignment rate, which is why umbrella take-home looks lower than an employee's on the same headline figure.
Take out the margin
The umbrella's margin is its fee, usually a fixed amount per week or per month rather than a percentage, so on a high rate it matters less than contractors expect and on a low rate it matters more. It should be stated as a figure in the illustration, not folded into a take-home percentage.
Then run PAYE on the gross
What remains is your gross pay, and the ordinary rules apply: your tax code against the £12,570 standard allowance, Income Tax at 20% to £50,270, 40% to £125,140 and 45% above, National Insurance at 8% between the primary threshold and the upper earnings limit and 2% above, and any student loan or pension you have.
Compare against the other routes on the same rate
Run the same rate through agency PAYE and, if the engagement is outside IR35, through a limited company. The three answers differ by the employer costs, the margin and the drawing plan, and seeing all three on one rate is the only way to know what you are being asked to give up.
Questions people ask about umbrella calculator
Why does an umbrella take home pay calculator show less than I expected?
Almost always because the quoted rate is the assignment rate, which funds employer National Insurance, holiday and the margin before your gross exists. Ask for a full illustration listing each of those lines, then compare offers on the same rate.
Is the umbrella margin a percentage?
Usually a fixed amount per week or per month. That means it takes a bigger share of a low rate than a high one, and it also means a percentage-based take-home promise tells you nothing about what the margin actually is.
Do umbrella companies pay different amounts of tax?
No. They all run the same PAYE rules on the same rates, so a materially higher take-home offered by one umbrella is a warning rather than an advantage. What legitimately differs is the margin and how holiday pay is handled.
Can a PAYE umbrella calculator compare both routes on one rate?
Yes, and you should. Agency PAYE has no umbrella margin but also no umbrella; the employer costs sit with the agency instead. The difference in your hand is usually the margin and the way holiday pay is funded.