Quote "Let's say you open an account for your minor child. You can deposit Rs 70,000 in your account and Rs 70,000 in your child's account. But you will only get the tax benefit on Rs 70,000" EndQuote
The combined limit for deposit (not just tax deduction) into PPF is 70,000 rupees per year for an individual and his/her guardians or minor children, taken together. So if Mr.X invests 40,000 rupees in the name of his child in PPF in a financial year, then Mr.X can invest at most only 30,000 rupees more in his own PPF account.
Please ask the author(s) of the article to check the rules and correct the information.
