In the year of election, an Interim budget is prepared with which the existing government has right to spend as per the interim budget only till March 2019. However, government can take vote on account to make expenditure as per the interim budget until the new government presents the full union budget.
The outgoing Government can make changes in tax law through interim budget. However, the new government has complete authority to make changes in the tax provisions and other estimates through the full budget presented by them.
The union budget on the other hand is full year budget which is effective for the complete financial year.