NSC provide net amount after 6 year as per interest rate mentioned at the time of NSC purchase (example- A bought NSC of Rs.10000/- at the rate of 8%, he will get Rs.16010/- after 6 year). But interest rate of PPF vary time to time, govt changes it year on year basis. My query is - If at the time of PPF a/c opening interest rate is 8% and after 1-year, it increases to 9% then which interest rate will be applicable? and what amount will investor get after 15 year?