Please look into this link for exact calculations.
TLDR: If you invest INR 1.5L between 1st April and 5th April of the FY, you will get maximum interest for the year due to how interests are calculated in PPF.
@gvze hey i just got started and did the wirh my icici acc. does interest get added to my amount every year by itself as a part of the balance in my ppf?
@iarunner 1.5L every fiscal year. You haven't put your 1.5L for this year yet right? The 10L that you put previous years won't be considered for tax exemption, only 1.5L you put this year.