How PPF interest is calculated
The Public Provident Fund (PPF) is a government-backed savings scheme you can open at a post office or bank. The government sets the interest rate every quarter. It's 7.1% a year for October to December 2026, the same as for many quarters before, but it can change, so the calculator lets you edit it.
Interest is worked out every month on the lowest balance between the 5th and the end of the month, and credited once a year at the end of March. So a deposit made by 5 April earns interest for the whole financial year. The calculator assumes you deposit the same amount by 5 April every year, which gives: closing balance = (opening balance + deposit) × (1 + rate).
Depositing the full ₹1,50,000 every year for 15 years at 7.1% puts in ₹22.5 lakh and grows to about ₹40.68 lakh, of which about ₹18.18 lakh is interest. Extending for 5 more years with deposits takes it to about ₹66.58 lakh, and 10 more years to just over ₹1 crore: compounding does most of its work in the later years.