15g filling date

See TDS is deductible at the time of maturity or at the time of credting interest into your account...in your case the interest amount is quite big, so most probable the bank will deduct TDS on accrual basis and therefore they will deduct TDS before 31-03-2013....so u have to submit 15G only once...and that too before the 31-03-2013...no need to submit it again after 31st March, as there will be no TDS next year.