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Employee on the Wrong NI Category H: How to Correct Previous Payroll Years

Found an employee incorrectly on NI category H? Learn when to send an additional FPS, how previous-year corrections work, and whether HMRC penalties are automatic.

You find it while checking payroll records: an employee has been on H rate National Insurance for almost three years. They were not eligible, the wrong category has gone through RTI, and now someone is asking the two questions every payroll team dreads:

Do we need to amend the FPS for previous years? And does this automatically mean a fine from HMRC?

The short answer is: correct it promptly, separate current-year and previous-year treatment, and keep a clear audit note. A wrong NI category can affect both employee and employer National Insurance, but HMRC guidance does not say that every payroll mistake automatically creates a penalty.

This article is general payroll guidance, not tax, legal, or accountancy advice. If the amounts are material, the error spans several years, or you are unsure how your software will submit the correction, check with HMRC, your accountant, or your payroll provider before submitting.

Quick answer

If an employee has incorrectly been on NI category H:

Check whether they were ever eligible for category H. GOV.UK says category H is for apprentices under 25.
Identify every affected tax year and pay period.
Recalculate National Insurance using the correct category letter and year-to-date figures.
For tax years between 6 April 2020 and 5 April 2026, HMRC says to send an additional FPS with the correct category letter and correct year-to-date National Insurance for that category.
For the current tax year, HMRC's guidance explains how to correct the category letter through your next FPS by reporting the incorrect and correct category details.
If the mistake caused an employee National Insurance overpayment or underpayment, correct the employee deduction position as well as the employer liability.
Keep a written record of what went wrong, when it was found, what was corrected, and who reviewed it.

What NI category H means

National Insurance category letters tell payroll software which employee and employer NIC rules to apply. Most employees are category A, but there are separate letters for particular groups.

Category H is not a general lower-rate category. GOV.UK lists category H for apprentices under 25.

That means two checks matter:

Was the employee genuinely an apprentice for the relevant periods?
Were they under 25 during the periods where category H was used?

If the answer is no, payroll may have calculated the wrong NICs. The correction may affect the employer's PAYE/NIC bill, the employee's deductions, or both, depending on the facts and the correct category.

Is this an amended FPS, an additional FPS, or an EYU?

In everyday payroll chat, people often call this an "amended FPS". HMRC's current guidance uses more specific wording.

For a wrong National Insurance category letter in the tax years between 6 April 2020 and 5 April 2026, HMRC says to send an additional FPS with the correct category letter and correct year-to-date National Insurance for that category.

That is the key route for the three-year scenario if the affected years sit inside that range.

If the error also affects the current tax year, handle that part separately. HMRC says that where the wrong category letter has been used in the current tax year, you report the mistake in your next FPS. The process includes reporting the incorrectly used category, entering the adjustment in the employee NICs field where relevant, adding the correct category letter, and entering the correct year-to-date National Insurance for the correct category.

The exact screens and workflow depend on your payroll software. If your software cannot submit the correction in the way HMRC expects, speak to the provider before trying to force a manual workaround.

What to do if the employee paid too much or too little NI

Do not stop at the RTI submission. Work out whether the wrong category caused an overpayment or underpayment of employee National Insurance.

If the employee paid too little, the position needs to be corrected. If they paid too much, you need to understand how the repayment will be handled and how it should appear in payroll. The same review should cover employer NICs and any PAYE account impact.

This is where an audit trail matters. Keep the recalculation, the original category used, the corrected category, the affected tax years, and the submission references together. If HMRC or the employee asks later, you want the story to be easy to follow.

Does HMRC automatically fine you?

No, not automatically.

HMRC's own guidance says you will only be charged a penalty for a mistake if you did not take reasonable care or did it deliberately.

That does not mean there is no risk. A three-year error is serious enough to review carefully. But the practical response is not panic. It is:

correct the records as soon as the issue is found;
pay any underpayment due to HMRC promptly;
document the cause of the error;
record the checks you have added to stop it happening again.

That evidence helps show reasonable care. Silence, delay, or repeated uncorrected mistakes are much harder to defend.

Practical checklist for a wrong NI category H correction

Use this before submitting anything:

Confirm whether the employee was ever eligible for category H.
Confirm the correct NI category for each affected period.
Split the correction by tax year.
Recalculate employee NICs and employer NICs.
Check whether the correction creates an employee overpayment or underpayment.
For tax years from 6 April 2020 to 5 April 2026, prepare the additional FPS with the correct category letter and correct year-to-date National Insurance.
For any current-year element, prepare the next FPS correction in line with HMRC's current-year category-letter guidance.
Review whether an EPS correction is needed for any separate EPS issue.
Pay HMRC any underpayment.
Keep an audit note explaining the error, the correction, the dates, the submissions, and the reviewer.

Why these mistakes happen

Wrong NI category errors usually do not happen because someone is careless for one day. They happen because employee status, apprenticeship details, payroll settings, timesheets, approvals, and RTI submissions live in different places.

One field is set up wrongly. Nobody spots it on the first payroll. Then the same setting rolls forward month after month until the problem becomes much bigger than it needed to be.

Workmax helps UK teams keep payroll records, approvals, timesheets, HMRC RTI submissions, and audit trails in one connected workflow. It also helps apply HMRC coding notices automatically, including tax code updates from P6, P9, and DPS notices, so payroll teams are not manually chasing every notice before the next run.

That does not replace checking unusual NI category changes, but it does reduce the amount of payroll data that has to be copied, rekeyed, and remembered across separate systems.

Want fewer payroll correction surprises? See how Workmax handles HMRC-recognised payroll, coding notices, RTI submissions, timesheets, and audit trails in one place.

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