Self-assessment is convenient and accessible. Filing a Self Assessment tax return is easy and convenient to do online as it lets you save your progress and return to it. is simple enough to do yourself if your finances are relatively simple and you know what you are doing. However, it can be time-consuming, and you may end up paying more tax than necessary if you aren’t sure about all the expenses and allowances you can claim. Self assessment services involve details of your untaxed income from the tax year, including income from self-employment, dividends and interest on shares. records of any expenses relating to self-employment. any contributions to charity or pensions that might be eligible for tax relief.