I worked as a full-time employee in the United Kingdom between January 2019 and June 2019. I noticed that the income tax and national insurance fees I paid for January-March were much, much lower than the ones I paid for April-June.
My employer told me that this is because the PAYE system calculates the withheld tax on a per annum basis. That is, they paid my monthly taxes expecting to be employed at their company for the rest of the tax year.
Should I file a tax refund? I am now a sole trader and will file a Self Assessment report, so I am not sure how I should handle this deduction claim.