The useful question is not what NI stands for
Most payslip guides work through the abbreviations. That is rarely what is wrong. Three things actually go wrong on payslips, and the first one you can check in about ten seconds.
Does it add up
Gross pay, minus every deduction the payslip lists, should equal the net. When it does not, money is leaving your pay that nothing on the document accounts for.
That matters because a payslip is legally required to itemise the amount and the purpose of every deduction. An unnamed one is exactly what section 13 of the Employment Rights Act 1996 makes unlawful, unless it is required by a statute, authorised by a written contract term you were given a copy of beforehand, or you agreed to it in writing in advance. Nothing about an employer being annoyed, or a till being short, or a uniform being unreturned changes that test.
It is a worker right, not an employee one
Section 8 opens with the words "a worker has the right to be given by his employer... a written itemised pay statement". Worker, not employee. The right was extended to all workers on 6 April 2019, which brought in zero-hours workers and agency workers who had previously been outside it.
This is worth knowing because a lot of people on casual contracts have simply never been given one and assume that is normal for the arrangement they are on. It is not.
The hours rule, and why it lands where it does
From the same date, section 8(2)(e) requires the number of hours to be shown wherever pay varies according to the time worked. They can appear as a single aggregate figure, or split by different types of work or different rates of pay.
Fixed hours do not have to be shown at all. Put those two together and the rule lands on exactly one group: the people whose pay changes every period. Which is precisely the group who cannot tell whether they have been paid correctly without the hours in front of them.
So a variable-hours payslip with no hours on it is two things at once, non-compliant and unauditable, and they are the same fact. If that is your payslip, asking for the hours is asking for the one piece of information that makes the rest of it checkable.
Tax that looks wrong, and National Insurance that is
These two behave completely differently, so work out which is which before you raise anything.
PAYE is cumulative. It looks at your income for the year so far, not just this period, and adjusts. So a bonus, a pay rise, a mid-year start or a code change all move a single month's tax legitimately, and one odd-looking month proves nothing. If it persists, the tax code is the thing to check.
National Insurance is not cumulative. It is worked out afresh each pay period, so on a steady salary it should not wander. A figure that is persistently out is more likely to be a genuine error, and the usual culprit is the NI category letter.
Keep them
Payslips are the evidence in a minimum wage complaint, an unlawful deduction claim, a mortgage application and a tax repayment. Your employer has no duty to give you copies of old ones once you have left, and payroll systems get replaced. The last payslip from every job you have had is worth more filing space than almost anything else in the drawer.
Common questions
My gross minus the deductions does not equal my net. What is going on?
Something is coming out that the payslip has not named, and that is worth asking about immediately. A payslip is legally required to itemise the amount and the purpose of every deduction. A deduction with no statutory basis, no written contract term you were given a copy of beforehand and no prior written agreement from you is an unlawful deduction under section 13 of the Employment Rights Act 1996.
Am I entitled to a payslip if I am on a zero-hours contract?
Yes. Section 8 of the Employment Rights Act 1996 says "a worker has the right" to an itemised pay statement, not "an employee", and the right was extended to all workers on 6 April 2019. That covers zero-hours workers and agency workers. If you have never received one, that is not how it is meant to work.
Does my payslip have to show my hours?
Only where your pay varies according to the time you work, but in that case yes, and it has been required since 6 April 2019 under section 8(2)(e). The hours can be a single total or split by type of work or rate of pay. Fixed hours do not have to be shown. So the requirement lands on precisely the payslip you cannot otherwise check, which is the point of it.
My tax looks too high this month. Is it wrong?
Not necessarily. PAYE is cumulative across the tax year rather than worked out afresh each period, so a bonus, a pay rise, a mid-year start or a change of tax code all move a single month legitimately. If it persists for several months, the tax code is the thing to check. National Insurance is different: it is calculated period by period, so on a steady salary it should not drift, and a persistent gap there is more likely to be a real problem.
What does the NI category letter mean?
It tells payroll which National Insurance rates to apply. A is the standard one that most employees are on. Others cover people over state pension age, apprentices under 25, and various reliefs. A wrong category letter is one of the more common causes of National Insurance that is persistently out, so ask about it if the figure never looks right.
There is no pension line on my payslip. Is that a problem?
Possibly. Automatic enrolment applies to anybody aged 22 to state pension age earning over £10,000, so no contribution is only correct for somebody genuinely outside that or who has actively opted out. Opt-outs also have to be re-run by the employer roughly every three years, and a good number of people are opted out without remembering choosing it.
How long should I keep payslips?
Longer than you think. They are the evidence for a minimum wage complaint, an unlawful deduction claim, a mortgage application and a tax repayment, and your employer has no duty to hand you copies of old ones once you have left. Keeping the last few years is sensible, and keeping the final one from every job is essential.