You can make a claim for the Employment Allowance up to 4 years after the end of the tax year in which the allowance applies. For example, if you want to make a claim for the allowance for the tax year 2015 to 2016 (that tax year ends on the 5 April 2016), you must make your claim by no later than the 5 April 2020.
You will need a separate Employment Payment Summary (EPS) for each year’s claim when claiming for any tax years that have now ended. You don’t need to send previously reported EPS figures, such as statutory payments.
If you send your claim one year after the tax year has ended, your claim will continue into the current tax year, unless you already have a claim for the Employment Allowance in place that year. If you have paid your PAYE up to date, HMRC will set any Employment Allowance award against your future or existing PAYE liabilities, unless you ask them to refund the amount.