You need to submit your employment allowance claim at the start of each tax year. 

If you've already stated you're not eligible for employment allowance in error, you'll need to change your claim.

 CAUTION: You can't claim employment allowance for a previous tax year in Sage Payroll. For guidance on this, contact HMRC via gov.uk. 

To submit your employment allowance claim

1. From the Summary tab, under HMRC Real Time Information (RTI) Scheme, select Submit Claim.

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2. Enter the details of your employment allowance claim.
    NOTE: Choose an industry sector before submitting your claim. If you aren’t sure what sector applies to your business, contact HMRC.  

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   Industry Sector	Agriculture Fisheries and Aquaculture Road Transport Industrial State Aid Rules Don’t Apply	Select the industry sector that applies to your business.  If none of the named sectors applies to you, select either: Industrial - if the state aid rules apply to your business  or State Aid Rules Don’t Apply - if your business doesn’t fall under state aid rules.
   State Aid Claimed €	0.00	You don’t need to enter this value. HMRC will check this for you.   The value appears in Euros because the European Commission sets the thresholds.

3. Select Next.
4. Confirm the details you're submitting to HMRC then select Submit.

You can view the status of your claim from the Summary tab.

HMRC notifies you within five working days if you don’t qualify for Employment Allowance.

The Employment Allowance Claim section can display the message:

"You’ve indicated that you aren’t eligible for Employment Allowance".

This message is now permanent. It doesn't stop you from claiming Employment Allowance.

I forgot to enter my Employment Allowance to date.