Can I invest INR 150,000 at the beginning of an financial year to avail the maximum interest from Sukanya Samriddhi Yojana or do I need to invest in a monthly basis with INR 12,500?

A Sukanya Samriddhi Account can be opened any time after the birth of a girl till she turns 10, with a minimum deposit of Rs 250 (Earlier it was Rs 1,000). In subsequent years, a minimum of Rs 250 and a maximum of Rs 1.5 lakh can be deposited during the ongoing financial year. 

As the interest is compounded annually, the more time you give your money to grow, the better will be the return. So it is better to invest 1.5 lakh at the beginning of the year than making monthly contributions for the same.