What this calculator doesn't know about you

You're thirtyish and you'd like to know how much of this to trust.

It assumes you're a UK taxpayer with one job, paid a regular salary. Where it can't see something, it says so rather than guessing.

What it works out today

• Income tax — England, Wales and Northern Ireland bands, or Scottish bands if you tell it you're a Scottish taxpayer. That includes the Personal Allowance, and the way it starts to disappear once you earn over £100,000.
• National Insurance — the standard employee rate, on the standard thresholds.
• A student loan deduction — Plans 1, 2, 4, 5 and Postgraduate, worked out per payslip rather than as a slice of your annual salary. If you tell it you don't know your plan, it leaves the deduction out and says so, rather than guessing.
• A workplace pension, under any of the three arrangements an employer can use — salary sacrifice, net pay, or relief at source. The same contribution changes your take-home by different amounts under each, which is the point of asking. If you don't know which one you're on, it leaves the pension out and tells you it has. How the three differ, and how to find out which is yours.
• A non-standard tax code — allowance codes, BR, D0 and D1, K codes, Scotland's S codes, Wales's C codes, and W1, M1 or X on the end. It applies the legal cap that stops any code taking more than half your pay. What the letters mean.
• One bonus, in one month. It shows you that payslip on its own, underneath the main answer, because a bonus month is not a typical month and shouldn't be averaged into one.

What it doesn't know yet

One thing, and it's about presentation rather than arithmetic.

• Weekly figures if you're paid weekly. It asks how often you're paid, and that genuinely changes your student loan deduction, which is worked out per payslip. But it still shows you the answer as a monthly figure.

What it isn't for

These aren't gaps to be filled in later. They're a different question.

• A second job or a second source of income. It looks at one salary at a time. If you're on a BR, D0 or D1 code this probably applies to you, and the calculator says so on screen.
• Being over State Pension age, which changes the National Insurance treatment.
• Self-employment. This is for salaried, employed pay.
• Pay that genuinely varies every month — regular overtime, shifts, irregular hours. It handles one bonus landing in one month. It isn't a model of a whole year of changing pay, and building one would need twelve months of figures I deliberately don't ask you for.
• The annual limits on pension contributions. There are caps on how much you can put into a pension with tax relief. This calculator doesn't know about them and won't warn you.

Why your first payslip after a pay rise can differ from this figure

Usually in your favour, and usually not by much.

The monthly figure this calculator gives you is what a typical month looks like once your new salary has been in place for a full tax year. If your rise lands part-way through a tax year, your first payslip or two afterwards can differ from it — usually in your favour — because of how PAYE spreads your tax-free allowance and your basic-rate band evenly across the twelve months of the year. By the end of the tax year this evens out.

For most rises the difference is nil. It only shows up when the rise takes you across a tax band, and even then it's usually a matter of tens of pounds in the first month or two, not an ongoing gap.

One thing you don't need to worry about

If you're under 21, your own National Insurance is unchanged.

Your employer pays a different rate for you. Yours is the same as everybody else's, so it makes no difference to the figure here. It's an easy thing to assume otherwise, which is the only reason it's worth saying at all.

A refund it can't work out for you

If a whole tax year came in under your threshold, some of what you repaid may be yours.

That's your income across a whole tax year, not any single payslip, and this calculator doesn't work it out. The Student Loans Company says it contacts people it identifies — but if a tax year has ended and you haven't heard from them, you can ask.

I can't tell you what to do about your own pay. I don't know your situation, and this is information rather than advice.

2026/27 tax year, from GOV.UK and the Scottish Government. Thresholds change every April.