Assessment year is the period that starts from 1 April and ends on 31 march. It is the year immediately succeeding the financial year wherein the income of the previous financial year is assessed. Government use assessment year for calculating tax on the previous year.

For example : If the current assessment year is 2015-16, which starts from I April 2015 and ends on 31 March 2016. To this assessment year financial year is 2014-15, starting from I April 2014 and ends on 31 March 2015. You will be calculating income tax for financial year in the assessment year.