Basis Period: timeframe during which a company or individual calculates their income for tax purposes. It typically starts from the day a business is set up or the start of the financial year, and it ends on the day before the anniversary of that date. It is generally a 12-month period preceding the YA.   Year of Assessment (YA): specific tax year in which you report your income and pay taxes on the income earned during your basis period. In Singapore, the Year of Assessment for individuals usually follows the calendar year (January 1st to December 31st). For companies, the Year of Assessment may differ and is determined by the company's financial year-end.   In summary, the basis period is the period for which income is calculated e.g. Year 2020, and the Year of Assessment is the year in which you declare and pay taxes on that income, e.g. Year 2021.