The following chart will help you to calculate NSC interest instantly. You can use the following NSC accrued interest chart as a calculator.
On certificates issued upto 31.3.2016 interest shall be compound half-yearly. The amount of interest accruing on a certificate of Rs. 100 shall be as follow:
NSC’s VIII Issue Interest Accrual Table Chart
Post Maturity Interest: Where on maturity, the amount has become due but not paid, it shall carry interest from the date of maturity up to the date of repayment at the prevailing POSB A/c rate.