FY is the year in which you earn an income. AY is the year following the financial year in which you have to evaluate the previous year’s income and pay taxes on it.

For instance, if your financial year is from 1 April 2019 to 31 March 2020, then it is known as FY 2019-20. The assessment year for the money earned during this period would begin after the financial year ends – that is from 1 April 2020 to 31 March 2021. Hence, the assessment year would be AY 2020-21.