Simple assessments are used in circumstances where there is a tax liability that can’t be collected automatically but where self-assessment is not required. Following the end of the tax year, HMRC sends a calculation (the simple assessment) detailing the amount to pay. You then check the calculation and, if happy, pay the amount by 31 January, or three months after the date on the letter (if later). If you opted for digital communication, you will probably have received your assessment for 2021/22 electronically. However, as it was not certain that this fulfilled HMRC’s obligations under the legislation, you may also receive a paper copy. It's important to note that this is not a demand for a payment, or that your original payment has gone missing. It is just to put beyond doubt that the assessment was served in a valid way. If you have already paid the amount shown, you don’t need to worry and you can quickly check this on your personal tax account.