How to calculate interest on NSC for a financial year when bought on a random date?

I have purchased Rs 150000 worth of National Savings Certificate at say 6,8% on August 21st 2021 and would like to calculate the interest earned on the same for the financial year 2021-22 for these 7 months and 12 days.  Is this how it is done?  or should i calculate one year's interest in August 21st 2022 and declare the same as my income for the financial year 2022-23 (and none from this investment this year)?

Thank you