filing return after 31st march 2019 for AY2018-2019

After March 31, 2019 you can't file your income tax return of Assessment Year 2018-19

There is no chance to file returns after 31st March, 2019.
You can't even file revised or belated returns after 31st March, 2019.

u cannot file your return after 31st March, 2019. 1 option is u file your return before 31st march, 2019 and then revise the return in case you have missed anything. After 31st march, you can file return only when a notice is issued to you by the income tax department.

If we can file return after receiving the department notice, How much penalty we should pay?

interest under sec 234A, 234B, 234C and penalty under sec 234F

can you please tell in terms of amount sir. for example if tax is Rs.300000/- ?

Working of Interest under sec 234A, 234B and 234C cannot be ascertained because there has to be seen various things such as amount paid as advance tax, date on which advance tax, Date on which returns will be filed.
But penalty under sec 234F shall be straight away Rs. 10,000 as your total income seems to be more than 5L

It is important to know the date on which returns shall be filed to calculate interest under sec 234A, 234B and 234C

You can use interest calculator available on income tax website

Thank you sir

you are welcome